Invoke WorkerScriptLoader's m_finishedCallback callback safely.

Source/web/WebSharedWorkerImpl.cpp

Index: Source/web/WebSharedWorkerImpl.cpp
diff --git a/Source/web/WebSharedWorkerImpl.cpp b/Source/web/WebSharedWorkerImpl.cpp
index 4481e1766bc38fa667a305f91cd7ceae84576926..6507cdeb987faf68d6915569f0d2f3badd693a5f 100644
--- a/Source/web/WebSharedWorkerImpl.cpp
+++ b/Source/web/WebSharedWorkerImpl.cpp
@@ -200,6 +200,8 @@ void WebSharedWorkerImpl::didFinishDocumentLoad(WebLocalFrame* frame)
         DenyCrossOriginRequests,
         bind(&WebSharedWorkerImpl::didReceiveScriptLoaderResponse, this),
         bind(&WebSharedWorkerImpl::onScriptLoaderFinished, this));
+    // Do nothing here since onScriptLoaderFinished() might have been already
+    // invoked and |this| might have been deleted at this point.
 }
 
 bool WebSharedWorkerImpl::isControlledByServiceWorker(WebDataSource& dataSource)