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diff --git a/base/i18n/streaming_utf8_validator.h b/base/i18n/streaming_utf8_validator.h
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+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// A streaming validator for UTF-8. Validation is based on the definition in
+// RFC-3629. In particular, it does not reject the invalid characters rejected
+// by base::IsStringUTF8().
+//
+// The implementation detects errors on the first possible byte.
+
+#ifndef BASE_I18N_STREAMING_UTF8_VALIDATOR_H_
+#define BASE_I18N_STREAMING_UTF8_VALIDATOR_H_
+
+#include <stddef.h>
+#include <stdint.h>
+
+#include <string>
+
+#include "base/i18n/base_i18n_export.h"
+#include "base/macros.h"
+
+namespace base {
+
+class BASE_I18N_EXPORT StreamingUtf8Validator {
+ public:
+  // The validator exposes 3 states. It starts in state VALID_ENDPOINT. As it
+  // processes characters it alternates between VALID_ENDPOINT and
+  // VALID_MIDPOINT. If it encounters an invalid byte or UTF-8 sequence the
+  // state changes permanently to INVALID.
+  enum State {
+    VALID_ENDPOINT,
+    VALID_MIDPOINT,
+    INVALID
+  };
+
+  StreamingUtf8Validator() : state_(0u) {}
+  // Trivial destructor intentionally omitted.
+
+  // Validate |size| bytes starting at |data|. If the concatenation of all calls
+  // to AddBytes() since this object was constructed or reset is a valid UTF-8
+  // string, returns VALID_ENDPOINT. If it could be the prefix of a valid UTF-8
+  // string, returns VALID_MIDPOINT. If an invalid byte or UTF-8 sequence was
+  // present, returns INVALID.
+  State AddBytes(const char* data, size_t size);
+
+  // Return the object to a freshly-constructed state so that it can be re-used.
+  void Reset();
+
+  // Validate a complete string using the same criteria. Returns true if the
+  // string only contains complete, valid UTF-8 codepoints.
+  static bool Validate(const std::string& string);
+
+ private:
+  // The current state of the validator. Value 0 is the initial/valid state.
+  // The state is stored as an offset into |kUtf8ValidatorTables|. The special
+  // state |kUtf8InvalidState| is invalid.
+  uint8_t state_;
+
+  // This type could be made copyable but there is currently no use-case for
+  // it.
+  DISALLOW_COPY_AND_ASSIGN(StreamingUtf8Validator);
+};
+
+}  // namespace base
+
+#endif  // BASE_I18N_STREAMING_UTF8_VALIDATOR_H_