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 399cec0a49383c2a42a63d2e9c9e0546c48a4dd2..9de867660f2cfa2fba17a015aaf949c1b39dad28 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;
@@ -171,6 +172,10 @@ public:
     virtual int webkitRequestAnimationFrame(FrameRequestCallback*) = 0;
     virtual void cancelAnimationFrame(int id) = 0;
 
+    // idle task extensions
+    virtual int requestIdleFrame(IdleRequestCallback*) = 0;
+    virtual void cancelIdleFrame(int id) = 0;
+
     void captureEvents() { }
     void releaseEvents() { }