Implement ReadableStream as a V8 extra

Source/bindings/core/v8/ScriptState.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 ScriptState_h
 #define ScriptState_h
 
 #include "bindings/core/v8/ScopedPersistent.h"
 #include "bindings/core/v8/V8PerContextData.h"
 #include "core/CoreExport.h"
@@ skipping 79 matching lines @@
     public:
         virtual ~Observer() { }
         virtual void willDisposeScriptState(ScriptState*) = 0;
     };
     void addObserver(Observer*);
     void removeObserver(Observer*);
 
     bool evalEnabled() const;
     void setEvalEnabled(bool);
     ScriptValue getFromGlobalObject(const char* name);
+    ScriptValue getFromExtrasExports(const char* name);
 
 protected:
     ScriptState(v8::Local<v8::Context>, PassRefPtr<DOMWrapperWorld>);
 
 private:
     v8::Isolate* m_isolate;
     // This persistent handle is weak.
     ScopedPersistent<v8::Context> m_context;
 
     // This RefPtr doesn't cause a cycle because all persistent handles that DOMWrapperWorld holds are weak.
@@ skipping 32 matching lines @@
     }
 
 private:
     RefPtr<ScriptState> m_scriptState;
     ScopedPersistent<v8::Context> m_context;
 };
 
 }
 
 #endif // ScriptState_h