Run Mutation Observer and Custom Element callbacks consistently at microtask checkpoint

Source/core/dom/Microtask.cpp

 /*
- * Copyright (C) 2012 Google Inc. All rights reserved.
+ * Copyright (C) 2013 Google Inc. All rights reserved.
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  * modification, are permitted provided that the following conditions
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  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
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  *    may be used to endorse or promote products derived from this
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-#ifndef RTCSessionDescriptionCallback_h
-#define RTCSessionDescriptionCallback_h
+#include "config.h"
+#include "core/dom/Microtask.h"
 
-#include "wtf/RefCounted.h"
+#include "core/dom/CustomElementCallbackDispatcher.h"
+#include "core/dom/MutationObserver.h"
+#include "wtf/Vector.h"
 
 namespace WebCore {
 
-class RTCSessionDescription;
+void Microtask::performCheckpoint()
+{
+    static bool performingCheckpoint = false;
+    if (performingCheckpoint)
+        return;
+    performingCheckpoint = true;
 
-class RTCSessionDescriptionCallback : public RefCounted<RTCSessionDescriptionCallback> {
-public:
-    virtual ~RTCSessionDescriptionCallback() { }
-    virtual bool handleEvent(RTCSessionDescription*) = 0;
-};
+    bool workToDo;
+    do {
+        MutationObserver::deliverAllMutations();
+        workToDo = CustomElementCallbackDispatcher::dispatcher().dispatch();

[rafaelw, 2013/06/24 23:15:49]

Nit: workToDo => anyWorkDone. 

Also, I think it's worth putting a TODO on the while loop that we ultimately
need this to be a FIFO queue.

+    } while (workToDo);
+
+    performingCheckpoint = false;
+}
 
 } // namespace WebCore
-
-#endif // RTCSessionDescriptionCallback_h