Implement requestIdleCallback API

Source/core/dom/IdleRequestCallback.h

+// Copyright 2015 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 IdleRequestCallback_h
+#define IdleRequestCallback_h
+
+#include "core/dom/ScriptedIdleTaskController.h"
+#include "platform/heap/Handle.h"
+
+namespace blink {
+
+class IdleRequestCallback : public GarbageCollectedFinalized<IdleRequestCallback> {
+public:
+    virtual ~IdleRequestCallback() { }
+    DEFINE_INLINE_VIRTUAL_TRACE() { }
+    virtual void handleEvent(double highResTimeMs, double deadlineTimeMs) = 0;
+
+    int m_id;
+    RefPtrWillBeMember<ScriptedIdleTaskController> m_controller;
+};
+
+}
+
+#endif // IdleRequestCallback_h