Flush microtask before event handlers are invoked

Source/bindings/v8/V8AbstractEventListener.cpp

Index: Source/bindings/v8/V8AbstractEventListener.cpp
diff --git a/Source/bindings/v8/V8AbstractEventListener.cpp b/Source/bindings/v8/V8AbstractEventListener.cpp
index d9b99058814ff9c6dcf7343f6aa549099ac6f7e2..9211d6eb799414f3fba529b7ddca512841fe738d 100644
--- a/Source/bindings/v8/V8AbstractEventListener.cpp
+++ b/Source/bindings/v8/V8AbstractEventListener.cpp
@@ -36,6 +36,7 @@
 #include "bindings/v8/V8Binding.h"
 #include "bindings/v8/V8EventListenerList.h"
 #include "bindings/v8/V8HiddenValue.h"
+#include "core/dom/Microtask.h"
 #include "core/events/BeforeUnloadEvent.h"
 #include "core/events/Event.h"
 #include "core/inspector/InspectorCounters.h"
@@ -109,6 +110,8 @@ void V8AbstractEventListener::invokeEventHandler(ExecutionContext* context, Even
         return;
     v8::Isolate* isolate = v8Context->GetIsolate();
 
+    Microtask::performCheckpoint(isolate);

[dominicc (has gone to gerrit), 2014/04/25 02:14:50]

Can you point to the DOM or HTML spec (...or all specs with event listeners?)
that says to do this?

[adamk, 2014/04/25 18:23:32]

I'm fairly sure this is not specced, and I'm not clear on where this requirement
came from. The attached bug has not details...

+
     v8::Local<v8::Value> returnValue;
     {
         // Catch exceptions thrown in the event handler so they do not propagate to javascript code that caused the event to fire.