Error Prone: 2.2.0 -> 2.3.1

This commit contains several other changes as part of the upgrade:

- Use -XepAllDisabledChecksAsWarnings to enable all available warnings so
  that we don't need to enable each warning explicitly.

- Remove explicit suppression of warnings in generated code, since
  -XepDisableWarningsInGeneratedCode is now sufficient to suppress all warnings
  in AutoValue and Protocol Buffer generated classes.

- Remove a suppression of "ConstructorLeaksThis", since
  https://github.com/google/error-prone/pull/789 was fixed.

- Fix a few occurrences of "FieldCanBeFinal".

3 files changed, 2 insertions, 5 deletions

diff --git a/api/src/main/java/io/opencensus/trace/CurrentSpanUtils.java b/api/src/main/java/io/opencensus/trace/CurrentSpanUtils.java
index a249d152..21511142 100644
--- a/api/src/main/java/io/opencensus/trace/CurrentSpanUtils.java
+++ b/api/src/main/java/io/opencensus/trace/CurrentSpanUtils.java
@@ -78,7 +78,7 @@ final class CurrentSpanUtils {
   private static final class ScopeInSpan implements Scope {
     private final Context origContext;
     private final Span span;
-    private boolean endSpan;
+    private final boolean endSpan;
 
     /**
      * Constructs a new {@link ScopeInSpan}.
diff --git a/api/src/test/java/io/opencensus/tags/TagContextTest.java b/api/src/test/java/io/opencensus/tags/TagContextTest.java
index 05473255..025c7bae 100644
--- a/api/src/test/java/io/opencensus/tags/TagContextTest.java
+++ b/api/src/test/java/io/opencensus/tags/TagContextTest.java
@@ -86,9 +86,6 @@ public final class TagContextTest {
   private static final class SimpleTagContext extends TagContext {
     @Nullable private final List<Tag> tags;
 
-    // This Error Prone warning doesn't seem correct, because the constructor is just calling
-    // another constructor.
-    @SuppressWarnings("ConstructorLeaksThis")
     SimpleTagContext(Tag... tags) {
       this(Lists.newArrayList(tags));
     }
diff --git a/api/src/test/java/io/opencensus/trace/SpanBuilderTest.java b/api/src/test/java/io/opencensus/trace/SpanBuilderTest.java
index a929ad97..839c8945 100644
--- a/api/src/test/java/io/opencensus/trace/SpanBuilderTest.java
+++ b/api/src/test/java/io/opencensus/trace/SpanBuilderTest.java
@@ -37,7 +37,7 @@ import org.mockito.MockitoAnnotations;
 // Need to suppress warnings for MustBeClosed because Java-6 does not support try-with-resources.
 @SuppressWarnings("MustBeClosedChecker")
 public class SpanBuilderTest {
-  private Tracer tracer = Tracing.getTracer();
+  private final Tracer tracer = Tracing.getTracer();
   @Mock private SpanBuilder spanBuilder;
   @Mock private Span span;