Run Mutation Observer and Custom Element callbacks consistently at microtask checkpoint

Source/core/dom/Microtask.h

Index: Source/core/dom/Microtask.h
diff --git a/Source/modules/mediastream/RTCSessionDescriptionCallback.idl b/Source/core/dom/Microtask.h
similarity index 86%
copy from Source/modules/mediastream/RTCSessionDescriptionCallback.idl
copy to Source/core/dom/Microtask.h
index e80be03efef811ef87092de3db6ebefd81c2ed7f..27f72cbec01e5795593d3e545a3b5ca3e5c046fa 100644
--- a/Source/modules/mediastream/RTCSessionDescriptionCallback.idl
+++ b/Source/core/dom/Microtask.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2012 Google Inc. All rights reserved.
+ * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
@@ -28,7 +28,19 @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
-callback interface RTCSessionDescriptionCallback {
-    boolean handleEvent(RTCSessionDescription sdp);
+#ifndef Microtask_h
+#define Microtask_h
+
+namespace WebCore {
+
+class Microtask {
+public:
+    static void performCheckpoint();
+
+private:
+    explicit Microtask();
 };
 
+}
+
+#endif // Microtask_h