Support structured clone atop v8::ValueSerializer behind a RuntimeEnabledFeature.

third_party/WebKit/Source/bindings/core/v8/ScriptValueSerializer.h

 // 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.
 
 #ifndef ScriptValueSerializer_h
 #define ScriptValueSerializer_h
 
 #include "bindings/core/v8/SerializationTag.h"
 #include "bindings/core/v8/SerializedScriptValue.h"
 #include "bindings/core/v8/V8Binding.h"
@@ skipping 465 matching lines @@
     }
 
     bool isEof() const { return m_position >= m_length; }
 
     ScriptState* getScriptState() const { return m_scriptState.get(); }
 
     virtual bool read(v8::Local<v8::Value>*, ScriptValueDeserializer&);
     bool readVersion(uint32_t& version);
     void setVersion(uint32_t);
 
+    // Used to extract the underlying buffer, in order to bypass
+    // SerializedScriptValueReader.
+    const uint8_t* buffer() const { return m_buffer; }
+    unsigned length() const { return m_length; }
+
 protected:
     v8::Isolate* isolate() const { return m_scriptState->isolate(); }
     v8::Local<v8::Context> context() const { return m_scriptState->context(); }
-    unsigned length() const { return m_length; }
     unsigned position() const { return m_position; }
 
     const uint8_t* allocate(uint32_t size)
     {
         const uint8_t* allocated = m_buffer + m_position;
         m_position += size;
         return allocated;
     }
 
     bool readWithTag(SerializationTag, v8::Local<v8::Value>*, ScriptValueDeserializer&);
@@ skipping 120 matching lines @@
     ArrayBufferContentsArray* m_arrayBufferContents;
     ImageBitmapContentsArray* m_imageBitmapContents;
     Vector<v8::Local<v8::Value>> m_arrayBuffers;
     Vector<v8::Local<v8::Value>> m_imageBitmaps;
     uint32_t m_version;
 };
 
 } // namespace blink
 
 #endif // ScriptValueSerializer_h