Implement requestIdleCallback API

Source/core/frame/DOMWindow.h

Index: Source/core/frame/DOMWindow.h
diff --git a/Source/core/frame/DOMWindow.h b/Source/core/frame/DOMWindow.h
index e5a8dadd68e1b15a1f2e70d76fce7fdcfb3cfa5f..1ef1cc9dd235aa52f66b3e5abac9988903c7fc10 100644
--- a/Source/core/frame/DOMWindow.h
+++ b/Source/core/frame/DOMWindow.h
@@ -28,6 +28,7 @@ class Element;
 class Frame;
 class FrameRequestCallback;
 class History;
+class IdleRequestCallback;
 class LocalDOMWindow;
 class MediaQueryList;
 class Navigator;
@@ -168,6 +169,10 @@ public:
     virtual int webkitRequestAnimationFrame(FrameRequestCallback*) = 0;
     virtual void cancelAnimationFrame(int id) = 0;
 
+    // Idle callback extensions
+    virtual int requestIdleCallback(IdleRequestCallback*, double timeoutMillis) = 0;
+    virtual void cancelIdleCallback(int id) = 0;
+
     void captureEvents() { }
     void releaseEvents() { }