Implement HTMLMediaElement::srcObject.

Source/core/html/MediaProvider.h

Index: Source/core/html/MediaProvider.h
diff --git a/Source/core/html/MediaProvider.h b/Source/core/html/MediaProvider.h
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+++ b/Source/core/html/MediaProvider.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.
+
+#ifndef MediaProvider_h
+#define MediaProvider_h
+
+#include "platform/heap/Handle.h"
+#include "wtf/Functional.h"
+
+namespace blink {
+
+class EventTarget;
+class MediaProvider;
+class ScriptValue;
+
+class MediaProvider : public WillBeGarbageCollectedMixin {
+public:
+    // Converter must be a static function and is used for converting between a ScriptValue and a MediaProvider instance.
+    // If the ScriptValue can not be converted to a MediaProvider, the function must return null.
+    typedef Function<MediaProvider*(const ScriptValue&)> Converter;
+    static MediaProvider* convert(const ScriptValue&);
+
+    MediaProvider(const String& interfaceName, const Converter&);
+    virtual ~MediaProvider() { }
+
+    virtual EventTarget* eventTarget() = 0;
+    virtual const String& getObjectUrl() = 0;
+
+    virtual void trace(Visitor*) { }
+};
+
+} // namespace blink
+
+#endif