[ABANDONED] Call Microtask::performCheckpoint for each worker task.

Source/bindings/v8/V8PerIsolateData.h

Index: Source/bindings/v8/V8PerIsolateData.h
diff --git a/Source/bindings/v8/V8PerIsolateData.h b/Source/bindings/v8/V8PerIsolateData.h
index 51490c231b71c9b9fdd27812a5c3726d5962ede5..6a727ff73597ea0f068eeab6ad89118326b98a81 100644
--- a/Source/bindings/v8/V8PerIsolateData.h
+++ b/Source/bindings/v8/V8PerIsolateData.h
@@ -93,6 +93,8 @@ public:
     bool hasInstance(const WrapperTypeInfo*, v8::Handle<v8::Value>);
     v8::Handle<v8::Object> findInstanceInPrototypeChain(const WrapperTypeInfo*, v8::Handle<v8::Value>);
 
+    // This method may return an empty handle when the script execution
+    // is terminated.
     v8::Local<v8::Context> ensureDomInJSContext();
 
     const char* previousSamplingState() const { return m_previousSamplingState; }