Onerror return value handling in workers fixed as per HTML5 spec.

Source/core/workers/WorkerMessagingProxy.cpp

Index: Source/core/workers/WorkerMessagingProxy.cpp
diff --git a/Source/core/workers/WorkerMessagingProxy.cpp b/Source/core/workers/WorkerMessagingProxy.cpp
index 3fc69d9d5270a50a7cca958e0dfba16a2b9b9880..1c72d7511c3758ca4315b4eaf9d046b657f4e47f 100644
--- a/Source/core/workers/WorkerMessagingProxy.cpp
+++ b/Source/core/workers/WorkerMessagingProxy.cpp
@@ -174,7 +174,8 @@ void WorkerMessagingProxy::reportException(const String& errorMessage, int lineN
     // This is intentionally different than the behavior in MessageWorkerTask, because terminated workers no longer deliver messages (section 4.6 of the WebWorker spec), but they do report exceptions.
 
     RefPtrWillBeRawPtr<ErrorEvent> event = ErrorEvent::create(errorMessage, sourceURL, lineNumber, columnNumber, 0);
-    bool errorHandled = !m_workerObject->dispatchEvent(event);
+    // Pass it on the error if "false" is returned, if "true" don't.
+    bool errorHandled = m_workerObject->dispatchEvent(event);
     if (!errorHandled)
         m_executionContext->reportException(event, 0, nullptr, NotSharableCrossOrigin);
 }