Flush microtask before event handlers are invoked

Source/core/dom/Microtask.h

Index: Source/core/dom/Microtask.h
diff --git a/Source/core/dom/Microtask.h b/Source/core/dom/Microtask.h
index 5bea815d0a98dad1e2d58875b41a32a0b9ae102c..c25ac4d660f02e5f04cb1a17ac95ff9e53a383d3 100644
--- a/Source/core/dom/Microtask.h
+++ b/Source/core/dom/Microtask.h
@@ -35,10 +35,15 @@
 #include "wtf/Functional.h"
 #include "wtf/PassOwnPtr.h"
 
+namespace v8 {
+class Isolate;
+}
+
 namespace WebCore {
 
 class Microtask {
 public:
+    static void performCheckpoint(v8::Isolate*);
     static void performCheckpoint();
     static void enqueueMicrotask(PassOwnPtr<blink::WebThread::Task>);
     static void enqueueMicrotask(const Closure&);