[WebView] Remove direct dependencies on hidden APIs.

BUG:18152150

Change-Id: If2b6c43f322b4223460b1be6c633858476244756

6 files changed, 444 insertions, 83 deletions

diff --git a/chromium/java/com/android/webview/chromium/DrawGLFunctor.java b/chromium/java/com/android/webview/chromium/DrawGLFunctor.java
index 7f7adeb..f955356 100644
--- a/chromium/java/com/android/webview/chromium/DrawGLFunctor.java
+++ b/chromium/java/com/android/webview/chromium/DrawGLFunctor.java
@@ -16,10 +16,12 @@
 
 package com.android.webview.chromium;
 
-import android.view.HardwareCanvas;
-import android.view.ViewRootImpl;
+import android.view.View;
+import android.graphics.Canvas;
 import android.util.Log;
 
+import com.android.webview.chromium.WebViewDelegateFactory.WebViewDelegate;
+
 import org.chromium.content.common.CleanupReference;
 
 // Simple Java abstraction and wrapper for the native DrawGLFunctor flow.
@@ -34,10 +36,12 @@ class DrawGLFunctor {
     // Pointer to native side instance
     private CleanupReference mCleanupReference;
     private DestroyRunnable mDestroyRunnable;
+    private WebViewDelegate mWebViewDelegate;
 
-    public DrawGLFunctor(long viewContext) {
-        mDestroyRunnable = new DestroyRunnable(nativeCreateGLFunctor(viewContext));
+    public DrawGLFunctor(long viewContext, WebViewDelegate webViewDelegate) {
+        mDestroyRunnable = new DestroyRunnable(nativeCreateGLFunctor(viewContext), webViewDelegate);
         mCleanupReference = new CleanupReference(this, mDestroyRunnable);
+        mWebViewDelegate = webViewDelegate;
     }
 
     public void destroy() {
@@ -46,6 +50,7 @@ class DrawGLFunctor {
             mCleanupReference.cleanupNow();
             mCleanupReference = null;
             mDestroyRunnable = null;
+            mWebViewDelegate = null;
         }
     }
 
@@ -53,26 +58,28 @@ class DrawGLFunctor {
         mDestroyRunnable.detachNativeFunctor();
     }
 
-    public boolean requestDrawGL(HardwareCanvas canvas, ViewRootImpl viewRootImpl,
+    public boolean requestDrawGL(Canvas canvas, View containerView,
             boolean waitForCompletion) {
         if (mDestroyRunnable.mNativeDrawGLFunctor == 0) {
             throw new RuntimeException("requested DrawGL on already destroyed DrawGLFunctor");
         }
-        if (viewRootImpl == null) {
-            // Can happen during teardown when window is leaked.
+
+        if (!mWebViewDelegate.canInvokeDrawGlFunctor(containerView)) {
             return false;
         }
 
-        mDestroyRunnable.mViewRootImpl = viewRootImpl;
+        mDestroyRunnable.mContainerView = containerView;
+
         if (canvas == null) {
-            viewRootImpl.invokeFunctor(mDestroyRunnable.mNativeDrawGLFunctor, waitForCompletion);
+            mWebViewDelegate.invokeDrawGlFunctor(containerView,
+                    mDestroyRunnable.mNativeDrawGLFunctor, waitForCompletion);
             return true;
         }
 
-        canvas.callDrawGLFunction(mDestroyRunnable.mNativeDrawGLFunctor);
+        mWebViewDelegate.callDrawGlFunction(canvas, mDestroyRunnable.mNativeDrawGLFunctor);
         if (waitForCompletion) {
-            viewRootImpl.invokeFunctor(mDestroyRunnable.mNativeDrawGLFunctor,
-                    waitForCompletion);
+            mWebViewDelegate.invokeDrawGlFunctor(containerView,
+                    mDestroyRunnable.mNativeDrawGLFunctor, waitForCompletion);
         }
         return true;
     }
@@ -85,10 +92,12 @@ class DrawGLFunctor {
     // IMPORTANT: this class must not hold any reference back to the outer DrawGLFunctor
     // instance, as that will defeat GC of that object.
     private static final class DestroyRunnable implements Runnable {
-        ViewRootImpl mViewRootImpl;
+        private WebViewDelegate mWebViewDelegate;
+        View mContainerView;
         long mNativeDrawGLFunctor;
-        DestroyRunnable(long nativeDrawGLFunctor) {
+        DestroyRunnable(long nativeDrawGLFunctor, WebViewDelegate webViewDelegate) {
             mNativeDrawGLFunctor = nativeDrawGLFunctor;
+            mWebViewDelegate = webViewDelegate;
         }
 
         // Called when the outer DrawGLFunctor instance has been GC'ed, i.e this is its finalizer.
@@ -100,10 +109,12 @@ class DrawGLFunctor {
         }
 
         void detachNativeFunctor() {
-            if (mNativeDrawGLFunctor != 0 && mViewRootImpl != null) {
-                mViewRootImpl.detachFunctor(mNativeDrawGLFunctor);
+            if (mNativeDrawGLFunctor != 0 && mContainerView != null
+                    && mWebViewDelegate != null) {
+                mWebViewDelegate.detachDrawGlFunctor(mContainerView, mNativeDrawGLFunctor);
             }
-            mViewRootImpl = null;
+            mContainerView = null;
+            mWebViewDelegate = null;
         }
     }
 
diff --git a/chromium/java/com/android/webview/chromium/ResourceRewriter.java b/chromium/java/com/android/webview/chromium/ResourceRewriter.java
index 683277a..7d035b7 100644
--- a/chromium/java/com/android/webview/chromium/ResourceRewriter.java
+++ b/chromium/java/com/android/webview/chromium/ResourceRewriter.java
@@ -17,7 +17,6 @@
 package com.android.webview.chromium;
 
 import android.content.Context;
-import android.util.SparseArray;
 
 /**
  * Helper class used to fix up resource ids.
@@ -27,29 +26,15 @@ import android.util.SparseArray;
  */
 class ResourceRewriter {
 
-    public static void rewriteRValues(Context ctx) {
-        // Rewrite the R 'constants' for the WebView library apk.
-        SparseArray<String> packageIdentifiers = ctx.getResources().getAssets()
-                .getAssignedPackageIdentifiers();
-
-        final int N = packageIdentifiers.size();
-        for (int i = 0; i < N; i++) {
-            final String name = packageIdentifiers.valueAt(i);
-
-            // The resources are always called com.android.webview even if the manifest has had the
-            // package renamed.
-            if ("com.android.webview".equals(name)) {
-                final int id = packageIdentifiers.keyAt(i);
-
-                // TODO: We should use jarjar to remove the redundant R classes here, but due
-                // to a bug in jarjar it's not possible to rename classes with '$' in their name.
-                // See b/15684775.
-                com.android.webview.chromium.R.onResourcesLoaded(id);
-                org.chromium.ui.R.onResourcesLoaded(id);
-                org.chromium.content.R.onResourcesLoaded(id);
-
-                break;
-            }
-        }
+    /**
+     * Rewrite the R 'constants' for the WebView library apk.
+     */
+    public static void rewriteRValues(final int packageId) {
+        // TODO: We should use jarjar to remove the redundant R classes here, but due
+        // to a bug in jarjar it's not possible to rename classes with '$' in their name.
+        // See b/15684775.
+        com.android.webview.chromium.R.onResourcesLoaded(packageId);
+        org.chromium.ui.R.onResourcesLoaded(packageId);
+        org.chromium.content.R.onResourcesLoaded(packageId);
     }
 }
diff --git a/chromium/java/com/android/webview/chromium/WebViewChromium.java b/chromium/java/com/android/webview/chromium/WebViewChromium.java
index c08eb41..fb31b2a 100644
--- a/chromium/java/com/android/webview/chromium/WebViewChromium.java
+++ b/chromium/java/com/android/webview/chromium/WebViewChromium.java
@@ -37,7 +37,6 @@ import android.print.PrintDocumentAdapter;
 import android.text.TextUtils;
 import android.util.Base64;
 import android.util.Log;
-import android.view.HardwareCanvas;
 import android.view.KeyEvent;
 import android.view.LayoutInflater;
 import android.view.MotionEvent;
@@ -166,8 +165,7 @@ class WebViewChromium implements WebViewProvider,
         mAppTargetSdkVersion = mWebView.getContext().getApplicationInfo().targetSdkVersion;
         mFactory = factory;
         mRunQueue = new WebViewChromiumRunQueue();
-        String webViewAssetPath = WebViewFactory.getLoadedPackageInfo().applicationInfo.sourceDir;
-        mWebView.getContext().getAssets().addAssetPath(webViewAssetPath);
+        factory.getWebViewDelegate().addWebViewAssetPath(mWebView.getContext());
     }
 
     static void completeWindowCreation(WebView parent, WebView child) {
@@ -244,7 +242,8 @@ class WebViewChromium implements WebViewProvider,
         final boolean areLegacyQuirksEnabled =
                 mAppTargetSdkVersion < Build.VERSION_CODES.KITKAT;
 
-        mContentsClientAdapter = new WebViewContentsClientAdapter(mWebView);
+        mContentsClientAdapter = new WebViewContentsClientAdapter(
+                mWebView, mFactory.getWebViewDelegate());
         mWebSettings = new ContentSettingsAdapter(new AwSettings(
                 mWebView.getContext(), isAccessFromFileURLsGrantedByDefault,
                 areLegacyQuirksEnabled));
@@ -2154,10 +2153,10 @@ class WebViewChromium implements WebViewProvider,
         public boolean requestDrawGL(Canvas canvas, boolean waitForCompletion,
                 View containerView) {
             if (mGLfunctor == null) {
-                mGLfunctor = new DrawGLFunctor(mAwContents.getAwDrawGLViewContext());
+                mGLfunctor = new DrawGLFunctor(mAwContents.getAwDrawGLViewContext(),
+                        mFactory.getWebViewDelegate());
             }
-            return mGLfunctor.requestDrawGL(
-                    (HardwareCanvas) canvas, containerView.getViewRootImpl(), waitForCompletion);
+            return mGLfunctor.requestDrawGL(canvas, containerView, waitForCompletion);
         }
 
         @Override
diff --git a/chromium/java/com/android/webview/chromium/WebViewChromiumFactoryProvider.java b/chromium/java/com/android/webview/chromium/WebViewChromiumFactoryProvider.java
index 8043ad8..af78843 100644
--- a/chromium/java/com/android/webview/chromium/WebViewChromiumFactoryProvider.java
+++ b/chromium/java/com/android/webview/chromium/WebViewChromiumFactoryProvider.java
@@ -19,7 +19,6 @@ package com.android.webview.chromium;
 import android.content.pm.PackageManager;
 import android.content.res.Resources;
 import android.app.ActivityManager;
-import android.app.ActivityThread;
 import android.content.ComponentCallbacks2;
 import android.content.Context;
 import android.content.Intent;
@@ -28,8 +27,6 @@ import android.net.Uri;
 import android.os.Build;
 import android.os.Looper;
 import android.os.StrictMode;
-import android.os.SystemProperties;
-import android.os.Trace;
 import android.util.Log;
 import android.webkit.CookieManager;
 import android.webkit.GeolocationPermissions;
@@ -41,6 +38,8 @@ import android.webkit.WebViewFactory;
 import android.webkit.WebViewFactoryProvider;
 import android.webkit.WebViewProvider;
 
+import com.android.webview.chromium.WebViewDelegateFactory.WebViewDelegate;
+
 import org.chromium.android_webview.AwBrowserContext;
 import org.chromium.android_webview.AwBrowserProcess;
 import org.chromium.android_webview.AwContents;
@@ -97,8 +96,24 @@ public class WebViewChromiumFactoryProvider implements WebViewFactoryProvider {
     private boolean mStarted;
 
     private SharedPreferences mWebViewPrefs;
+    private WebViewDelegate mWebViewDelegate;
 
+    /**
+     * Constructor called by the API 21 version of {@link WebViewFactory} and earlier.
+     */
     public WebViewChromiumFactoryProvider() {
+        initialize(WebViewDelegateFactory.createApi21CompatibilityDelegate());
+    }
+
+    /**
+     * Constructor called by the API 22 version of {@link WebViewFactory} and later.
+     */
+    public WebViewChromiumFactoryProvider(android.webkit.WebViewDelegate delegate) {
+        initialize(WebViewDelegateFactory.createProxyDelegate(delegate));
+    }
+
+    private void initialize(WebViewDelegate webViewDelegate) {
+        mWebViewDelegate = webViewDelegate;
         if (isBuildDebuggable()) {
             // Suppress the StrictMode violation as this codepath is only hit on debugglable builds.
             StrictMode.ThreadPolicy oldPolicy = StrictMode.allowThreadDiskReads();
@@ -117,21 +132,19 @@ public class WebViewChromiumFactoryProvider implements WebViewFactoryProvider {
 
         ThreadUtils.setWillOverrideUiThread();
         // Load chromium library.
-        Trace.traceBegin(Trace.TRACE_TAG_WEBVIEW, "AwBrowserProcess.loadLibrary()");
         AwBrowserProcess.loadLibrary();
-        Trace.traceEnd(Trace.TRACE_TAG_WEBVIEW);
         // Load glue-layer support library.
         System.loadLibrary("webviewchromium_plat_support");
 
         // Use shared preference to check for package downgrade.
-        mWebViewPrefs = ActivityThread.currentApplication().getSharedPreferences(
+        mWebViewPrefs = mWebViewDelegate.getApplication().getSharedPreferences(
                             CHROMIUM_PREFS_NAME, Context.MODE_PRIVATE);
         int lastVersion = mWebViewPrefs.getInt(VERSION_CODE_PREF, 0);
         int currentVersion = WebViewFactory.getLoadedPackageInfo().versionCode;
         if (lastVersion > currentVersion) {
             // The WebView package has been downgraded since we last ran in this application.
             // Delete the WebView data directory's contents.
-            String dataDir = PathUtils.getDataDirectory(ActivityThread.currentApplication());
+            String dataDir = PathUtils.getDataDirectory(mWebViewDelegate.getApplication());
             Log.i(TAG, "WebView package downgraded from " + lastVersion + " to " + currentVersion +
                        "; deleting contents of " + dataDir);
             deleteContents(new File(dataDir));
@@ -166,21 +179,6 @@ public class WebViewChromiumFactoryProvider implements WebViewFactoryProvider {
         AwContents.setAwDrawGLFunctionTable(GraphicsUtils.getDrawGLFunctionTable());
     }
 
-    private static void initTraceEvent() {
-        syncATraceState();
-        SystemProperties.addChangeCallback(new Runnable() {
-            @Override
-            public void run() {
-                syncATraceState();
-            }
-        });
-    }
-
-    private static void syncATraceState() {
-        long enabledFlags = SystemProperties.getLong("debug.atrace.tags.enableflags", 0);
-        TraceEvent.setATraceEnabled((enabledFlags & Trace.TRACE_TAG_WEBVIEW) != 0);
-    }
-
     private void ensureChromiumStartedLocked(boolean onMainThread) {
         assert Thread.holdsLock(mLock);
 
@@ -250,15 +248,22 @@ public class WebViewChromiumFactoryProvider implements WebViewFactoryProvider {
                 "/system/framework/webview/paks");
 
         // Make sure that ResourceProvider is initialized before starting the browser process.
-        setUpResources(ActivityThread.currentApplication());
+        setUpResources(mWebViewDelegate.getApplication());
         initPlatSupportLibrary();
-        AwBrowserProcess.start(ActivityThread.currentApplication());
+        AwBrowserProcess.start(mWebViewDelegate.getApplication());
 
         if (Build.IS_DEBUGGABLE) {
             setWebContentsDebuggingEnabled(true);
         }
 
-        initTraceEvent();
+        TraceEvent.setATraceEnabled(mWebViewDelegate.isTraceTagEnabled());
+        mWebViewDelegate.setOnTraceEnabledChangeListener(
+                new WebViewDelegate.OnTraceEnabledChangeListener() {
+                    @Override
+                    public void onTraceEnabledChange(boolean enabled) {
+                        TraceEvent.setATraceEnabled(enabled);
+                    }
+                });
         mStarted = true;
 
         for (WeakReference<WebViewChromium> wvc : mWebViewsToStart) {
@@ -309,10 +314,13 @@ public class WebViewChromiumFactoryProvider implements WebViewFactoryProvider {
         mDevToolsServer.setRemoteDebuggingEnabled(enable);
     }
 
-    private void setUpResources(Context ctx) {
-        ResourceRewriter.rewriteRValues(ctx);
+    private void setUpResources(Context context) {
+        // The resources are always called com.android.webview even if the manifest has had the
+        // package renamed.
+        ResourceRewriter.rewriteRValues(
+                mWebViewDelegate.getPackageId(context.getResources(), "com.android.webview"));
 
-        AwResource.setResources(ctx.getResources());
+        AwResource.setResources(context.getResources());
         AwResource.setErrorPageResources(android.R.raw.loaderror,
                 android.R.raw.nodomain);
         AwResource.setConfigKeySystemUuidMapping(
@@ -410,7 +418,7 @@ public class WebViewChromiumFactoryProvider implements WebViewFactoryProvider {
                     // will bring up just the parts it needs to make this work on a temporary
                     // basis until Chromium is started for real. The temporary cookie manager
                     // needs the application context to have been set.
-                    ContentMain.initApplicationContext(ActivityThread.currentApplication());
+                    ContentMain.initApplicationContext(mWebViewDelegate.getApplication());
                 }
                 mCookieManager = new CookieManagerAdapter(new AwCookieManager());
             }
@@ -453,4 +461,8 @@ public class WebViewChromiumFactoryProvider implements WebViewFactoryProvider {
         }
         return mWebViewDatabase;
     }
+
+    WebViewDelegate getWebViewDelegate() {
+        return mWebViewDelegate;
+    }
 }
diff --git a/chromium/java/com/android/webview/chromium/WebViewContentsClientAdapter.java b/chromium/java/com/android/webview/chromium/WebViewContentsClientAdapter.java
index 24c0ebc..6b4b894 100644
--- a/chromium/java/com/android/webview/chromium/WebViewContentsClientAdapter.java
+++ b/chromium/java/com/android/webview/chromium/WebViewContentsClientAdapter.java
@@ -24,7 +24,6 @@ import android.graphics.BitmapFactory;
 import android.graphics.Canvas;
 import android.graphics.Color;
 import android.graphics.Picture;
-import android.net.http.ErrorStrings;
 import android.net.http.SslError;
 import android.net.Uri;
 import android.os.Build;
@@ -52,6 +51,8 @@ import android.webkit.WebResourceRequest;
 import android.webkit.WebView;
 import android.webkit.WebViewClient;
 
+import com.android.webview.chromium.WebViewDelegateFactory.WebViewDelegate;
+
 import org.chromium.android_webview.AwContentsClient;
 import org.chromium.android_webview.AwContentsClientBridge;
 import org.chromium.android_webview.AwHttpAuthHandler;
@@ -107,6 +108,8 @@ public class WebViewContentsClientAdapter extends AwContentsClient {
     // The listener receiving notifications of screen updates.
     private WebView.PictureListener mPictureListener;
 
+    private WebViewDelegate mWebViewDelegate;
+
     private DownloadListener mDownloadListener;
 
     private Handler mUiThreadHandler;
@@ -120,12 +123,13 @@ public class WebViewContentsClientAdapter extends AwContentsClient {
      *
      * @param webView the {@link WebView} instance that this adapter is serving.
      */
-    WebViewContentsClientAdapter(WebView webView) {
-        if (webView == null) {
-            throw new IllegalArgumentException("webView can't be null");
+    WebViewContentsClientAdapter(WebView webView, WebViewDelegate webViewDelegate) {
+        if (webView == null || webViewDelegate == null) {
+            throw new IllegalArgumentException("webView or delegate can't be null");
         }
 
         mWebView = webView;
+        mWebViewDelegate = webViewDelegate;
         setWebViewClient(null);
 
         mUiThreadHandler = new Handler() {
@@ -531,7 +535,7 @@ public class WebViewContentsClientAdapter extends AwContentsClient {
             // ErrorStrings is @hidden, so we can't do this in AwContents.
             // Normally the net/ layer will set a valid description, but for synthesized callbacks
             // (like in the case for intercepted requests) AwContents will pass in null.
-            description = ErrorStrings.getString(errorCode, mWebView.getContext());
+            description = mWebViewDelegate.getErrorString(mWebView.getContext(), errorCode);
         }
         TraceEvent.begin();
         if (TRACE) Log.d(TAG, "onReceivedError=" + failingUrl);
diff --git a/chromium/java/com/android/webview/chromium/WebViewDelegateFactory.java b/chromium/java/com/android/webview/chromium/WebViewDelegateFactory.java
new file mode 100644
index 0000000..f5d1518
--- /dev/null
+++ b/chromium/java/com/android/webview/chromium/WebViewDelegateFactory.java
@@ -0,0 +1,350 @@
+package com.android.webview.chromium;
+
+import android.app.ActivityThread;
+import android.app.Application;
+import android.content.Context;
+import android.content.pm.PackageInfo;
+import android.content.res.AssetManager;
+import android.content.res.Resources;
+import android.graphics.Canvas;
+import android.net.http.ErrorStrings;
+import android.os.SystemProperties;
+import android.os.Trace;
+import android.util.Log;
+import android.util.SparseArray;
+import android.view.HardwareCanvas;
+import android.view.View;
+import android.view.ViewRootImpl;
+import android.webkit.WebViewFactory;
+
+import java.lang.reflect.InvocationTargetException;
+import java.lang.reflect.Method;
+
+/**
+ * Factory class for {@link WebViewDelegate com.android.webview.chromium.WebViewDelegate}s.
+ *
+ * <p>{@link WebViewDelegate com.android.webview.chromium.WebViewDelegate}s provide the same
+ * interface as {@link android.webkit.WebViewDelegate android.webkit.WebViewDelegate} but without
+ * a dependency on the webkit class. Defining our own
+ * {@link WebViewDelegate com.android.webview.chromium.WebViewDelegate} in frameworks/webview
+ * allows the WebView apk to be binary compatible with the API 21 version of the framework, in
+ * which {@link android.webkit.WebViewDelegate android.webkit.WebViewDelegate} had not yet been
+ * introduced.
+ *
+ * <p>The {@link WebViewDelegate com.android.webview.chromium.WebViewDelegate} interface and this
+ * factory class can be removed once we don't longer need to support WebView apk updates to devices
+ * running the API 21 version of the framework. At that point, we should use
+ * {@link android.webkit.WebViewDelegate android.webkit.WebViewDelegate} directly instead.
+ */
+class WebViewDelegateFactory {
+
+    /**
+     * Copy of {@link android.webkit.WebViewDelegate android.webkit.WebViewDelegate}'s interface.
+     * See {@link WebViewDelegateFactory} for the reasons why this copy is needed.
+     */
+    interface WebViewDelegate {
+        /** @see android.webkit.WebViewDelegate.OnTraceEnabledChangeListener */
+        interface OnTraceEnabledChangeListener {
+            void onTraceEnabledChange(boolean enabled);
+        }
+
+        /** @see android.webkit.WebViewDelegate#setOnTraceEnabledChangeListener */
+        void setOnTraceEnabledChangeListener(final OnTraceEnabledChangeListener listener);
+
+        /** @see android.webkit.WebViewDelegate#isTraceTagEnabled */
+        boolean isTraceTagEnabled();
+
+        /** @see android.webkit.WebViewDelegate#canInvokeDrawGlFunctor */
+        boolean canInvokeDrawGlFunctor(View containerView);
+
+        /** @see android.webkit.WebViewDelegate#invokeDrawGlFunctor */
+        void invokeDrawGlFunctor(View containerView, long nativeDrawGLFunctor,
+                boolean waitForCompletion);
+
+        /** @see android.webkit.WebViewDelegate#callDrawGlFunction */
+        void callDrawGlFunction(Canvas canvas, long nativeDrawGLFunctor);
+
+        /** @see android.webkit.WebViewDelegate#detachDrawGlFunctor */
+        void detachDrawGlFunctor(View containerView, long nativeDrawGLFunctor);
+
+        /** @see android.webkit.WebViewDelegate#getPackageId */
+        int getPackageId(Resources resources, String packageName);
+
+        /** @see android.webkit.WebViewDelegate#getApplication */
+        Application getApplication();
+
+        /** @see android.webkit.WebViewDelegate#getErrorString */
+        String getErrorString(Context context, int errorCode);
+
+        /** @see android.webkit.WebViewDelegate#addWebViewAssetPath */
+        void addWebViewAssetPath(Context context);
+    }
+
+    /**
+     * Creates a {@link WebViewDelegate com.android.webview.chromium.WebViewDelegate} that proxies
+     * requests to the given {@link android.webkit.WebViewDelegate android.webkit.WebViewDelegate}.
+     *
+     * @return the created delegate
+     */
+    static WebViewDelegate createProxyDelegate(android.webkit.WebViewDelegate delegate) {
+        return new ProxyDelegate(delegate);
+    }
+
+    /**
+     * Creates a {@link WebViewDelegate com.android.webview.chromium.WebViewDelegate} compatible
+     * with the API 21 version of the framework in which
+     * {@link android.webkit.WebViewDelegate android.webkit.WebViewDelegate} had not yet been
+     * introduced.
+     *
+     * @return the created delegate
+     */
+    static WebViewDelegate createApi21CompatibilityDelegate() {
+        return new Api21CompatibilityDelegate();
+    }
+
+    /**
+     * A {@link WebViewDelegate com.android.webview.chromium.WebViewDelegate} that proxies requests
+     * to a {@link android.webkit.WebViewDelegate android.webkit.WebViewDelegate}.
+     */
+    private static class ProxyDelegate implements WebViewDelegate {
+
+        android.webkit.WebViewDelegate delegate;
+
+        ProxyDelegate(android.webkit.WebViewDelegate delegate) {
+            this.delegate = delegate;
+        }
+
+        @Override
+        public void setOnTraceEnabledChangeListener(final OnTraceEnabledChangeListener listener) {
+            delegate.setOnTraceEnabledChangeListener(
+                    new android.webkit.WebViewDelegate.OnTraceEnabledChangeListener() {
+                        @Override
+                        public void onTraceEnabledChange(boolean enabled) {
+                            listener.onTraceEnabledChange(enabled);
+                            ;
+                        }
+                    });
+        }
+
+        @Override
+        public boolean isTraceTagEnabled() {
+            return delegate.isTraceTagEnabled();
+        }
+
+        @Override
+        public boolean canInvokeDrawGlFunctor(View containerView) {
+            return delegate.canInvokeDrawGlFunctor(containerView);
+        }
+
+        @Override
+        public void invokeDrawGlFunctor(View containerView, long nativeDrawGLFunctor,
+                boolean waitForCompletion) {
+            delegate.invokeDrawGlFunctor(containerView, nativeDrawGLFunctor, waitForCompletion);
+        }
+
+        @Override
+        public void callDrawGlFunction(Canvas canvas, long nativeDrawGLFunctor) {
+            delegate.callDrawGlFunction(canvas, nativeDrawGLFunctor);
+        }
+
+        @Override
+        public void detachDrawGlFunctor(View containerView, long nativeDrawGLFunctor) {
+            delegate.detachDrawGlFunctor(containerView, nativeDrawGLFunctor);
+        }
+
+        @Override
+        public int getPackageId(Resources resources, String packageName) {
+            return delegate.getPackageId(resources, packageName);
+        }
+
+        @Override
+        public Application getApplication() {
+            return delegate.getApplication();
+        }
+
+        @Override
+        public String getErrorString(Context context, int errorCode) {
+            return delegate.getErrorString(context, errorCode);
+        }
+
+        @Override
+        public void addWebViewAssetPath(Context context) {
+            delegate.addWebViewAssetPath(context);
+        }
+    }
+
+    /**
+     * A {@link WebViewDelegate com.android.webview.chromium.WebViewDelegate} compatible with the
+     * API 21 version of the framework in which
+     * {@link android.webkit.WebViewDelegate android.webkit.WebViewDelegate} had not yet been
+     * introduced.
+     *
+     * <p>This class implements the
+     * {@link WebViewDelegate com.android.webview.chromium.WebViewDelegate} functionality by using
+     * reflection to call into hidden frameworks APIs released in the API-21 version of the
+     * framework.
+     */
+    private static class Api21CompatibilityDelegate implements WebViewDelegate {
+        /** Copy of Trace.TRACE_TAG_WEBVIEW */
+        private final static long TRACE_TAG_WEBVIEW = 1L << 4;
+
+        /** Hidden APIs released in the API 21 version of the framework */
+        private final Method mIsTagEnabledMethod;
+        private final Method mAddChangeCallbackMethod;
+        private final Method mGetViewRootImplMethod;
+        private final Method mInvokeFunctorMethod;
+        private final Method mCallDrawGLFunctionMethod;
+        private final Method mDetachFunctorMethod;
+        private final Method mGetAssignedPackageIdentifiersMethod;
+        private final Method mAddAssetPathMethod;
+        private final Method mCurrentApplicationMethod;
+        private final Method mGetStringMethod;
+        private final Method mGetLoadedPackageInfoMethod;
+
+        Api21CompatibilityDelegate() {
+            try {
+                // Important: This reflection essentially defines a snapshot of some hidden APIs
+                // at version 21 of the framework for compatibility reasons, and the reflection
+                // should not be changed even if those hidden APIs change in future releases.
+                mIsTagEnabledMethod = Trace.class.getMethod("isTagEnabled", long.class);
+                mAddChangeCallbackMethod = Class.forName("android.os.SystemProperties")
+                        .getMethod("addChangeCallback", Runnable.class);
+                mGetViewRootImplMethod = View.class.getMethod("getViewRootImpl");
+                mInvokeFunctorMethod = Class.forName("android.view.ViewRootImpl")
+                        .getMethod("invokeFunctor", long.class, boolean.class);
+                mDetachFunctorMethod = Class.forName("android.view.ViewRootImpl")
+                        .getMethod("detachFunctor", long.class);
+                mCallDrawGLFunctionMethod = Class.forName("android.view.HardwareCanvas")
+                        .getMethod("callDrawGLFunction", long.class);
+                mGetAssignedPackageIdentifiersMethod = AssetManager.class.getMethod(
+                        "getAssignedPackageIdentifiers");
+                mAddAssetPathMethod = AssetManager.class.getMethod(
+                        "addAssetPath", String.class);
+                mCurrentApplicationMethod = Class.forName("android.app.ActivityThread")
+                        .getMethod("currentApplication");
+                mGetStringMethod = Class.forName("android.net.http.ErrorStrings")
+                        .getMethod("getString", int.class, Context.class);
+                mGetLoadedPackageInfoMethod = Class.forName("android.webkit.WebViewFactory")
+                        .getMethod("getLoadedPackageInfo");
+            } catch (Exception e) {
+                throw new RuntimeException("Invalid reflection", e);
+            }
+        }
+
+        @Override
+        public void setOnTraceEnabledChangeListener(final OnTraceEnabledChangeListener listener) {
+            try {
+                mAddChangeCallbackMethod.invoke(null, new Runnable() {
+                    @Override
+                    public void run() {
+                        listener.onTraceEnabledChange(isTraceTagEnabled());
+                    }
+                });
+            } catch (Exception e) {
+                throw new RuntimeException("Invalid reflection", e);
+            }
+        }
+
+        @Override
+        public boolean isTraceTagEnabled() {
+            try {
+                return ((Boolean) mIsTagEnabledMethod.invoke(null, TRACE_TAG_WEBVIEW));
+            } catch (Exception e) {
+                throw new RuntimeException("Invalid reflection", e);
+            }
+        }
+
+        @Override
+        public boolean canInvokeDrawGlFunctor(View containerView) {
+            try {
+                Object viewRootImpl = mGetViewRootImplMethod.invoke(containerView);
+                 // viewRootImpl can be null during teardown when window is leaked.
+                return viewRootImpl != null;
+            } catch (Exception e) {
+                throw new RuntimeException("Invalid reflection", e);
+            }
+        }
+
+        @Override
+        public void invokeDrawGlFunctor(View containerView, long nativeDrawGLFunctor,
+                boolean waitForCompletion) {
+            try {
+                Object viewRootImpl = mGetViewRootImplMethod.invoke(containerView);
+                if (viewRootImpl != null) {
+                    mInvokeFunctorMethod.invoke(viewRootImpl, nativeDrawGLFunctor, waitForCompletion);
+                }
+            } catch (Exception e) {
+                throw new RuntimeException("Invalid reflection", e);
+            }
+        }
+
+        @Override
+        public void callDrawGlFunction(Canvas canvas, long nativeDrawGLFunctor) {
+            try {
+                mCallDrawGLFunctionMethod.invoke(canvas, nativeDrawGLFunctor);
+            } catch (Exception e) {
+                throw new RuntimeException("Invalid reflection", e);
+            }
+        }
+
+        @Override
+        public void detachDrawGlFunctor(View containerView, long nativeDrawGLFunctor) {
+            try {
+                Object viewRootImpl = mGetViewRootImplMethod.invoke(containerView);
+                if (viewRootImpl != null) {
+                    mDetachFunctorMethod.invoke(viewRootImpl, nativeDrawGLFunctor);
+                }
+            } catch (Exception e) {
+                throw new RuntimeException("Invalid reflection", e);
+            }
+        }
+
+        @Override
+        public int getPackageId(Resources resources, String packageName) {
+            try {
+                SparseArray packageIdentifiers =
+                        (SparseArray) mGetAssignedPackageIdentifiersMethod.invoke(
+                                resources.getAssets());
+                for (int i = 0; i < packageIdentifiers.size(); i++) {
+                    final String name = (String) packageIdentifiers.valueAt(i);
+
+                    if (packageName.equals(name)) {
+                        return packageIdentifiers.keyAt(i);
+                    }
+                }
+            } catch (Exception e) {
+                throw new RuntimeException("Invalid reflection", e);
+            }
+            throw new RuntimeException("Package not found: " + packageName);
+        }
+
+        @Override
+        public Application getApplication() {
+            try {
+                return (Application) mCurrentApplicationMethod.invoke(null);
+            } catch (Exception e) {
+                throw new RuntimeException("Invalid reflection", e);
+            }
+        }
+
+        @Override
+        public String getErrorString(Context context, int errorCode) {
+            try {
+                return (String) mGetStringMethod.invoke(null, errorCode, context);
+            } catch (Exception e) {
+                throw new RuntimeException("Invalid reflection", e);
+            }
+        }
+
+        @Override
+        public void addWebViewAssetPath(Context context) {
+            try {
+                PackageInfo info = (PackageInfo) mGetLoadedPackageInfoMethod.invoke(null);
+                mAddAssetPathMethod.invoke(context.getAssets(), info.applicationInfo.sourceDir);
+            } catch (Exception e) {
+                throw new RuntimeException("Invalid reflection", e);
+            }
+        }
+    }
+}
+