Run Mutation Observer and Custom Element callbacks consistently at microtask checkpoint

Source/core/dom/Microtask.cpp

Index: Source/core/dom/Microtask.cpp
diff --git a/Source/modules/mediastream/RTCSessionDescriptionCallback.h b/Source/core/dom/Microtask.cpp
similarity index 72%
copy from Source/modules/mediastream/RTCSessionDescriptionCallback.h
copy to Source/core/dom/Microtask.cpp
index 678daa7b0d0de42a2dc4f0b115412f71b1755d6b..cb0b12b618b570e67dee34c4aeb1aea6560b940f 100644
--- a/Source/modules/mediastream/RTCSessionDescriptionCallback.h
+++ b/Source/core/dom/Microtask.cpp
@@ -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
@@ -28,21 +28,29 @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
-#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 anyWorkDone;
+    do {
+        MutationObserver::deliverAllMutations();
+        anyWorkDone = CustomElementCallbackDispatcher::instance().dispatch();
+    } while (anyWorkDone);
 
-} // namespace WebCore
+    performingCheckpoint = false;
+}
 
-#endif // RTCSessionDescriptionCallback_h
+} // namespace WebCore