ServiceWorker: Add null check of ExecutionContext in skipWaiting.

Source/modules/serviceworkers/ServiceWorkerGlobalScope.cpp

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 108 matching lines @@
     return m_clients;
 }
 
 void ServiceWorkerGlobalScope::close(ExceptionState& exceptionState)
 {
     exceptionState.throwDOMException(InvalidAccessError, "Not supported.");
 }
 
 ScriptPromise ServiceWorkerGlobalScope::skipWaiting(ScriptState* scriptState)
 {
+    ExecutionContext* executionContext = scriptState->executionContext();
+    // FIXME: short-term fix, see details at: https://codereview.chromium.org/535193002/.
+    if (!executionContext)
+        return ScriptPromise();
+
     RefPtrWillBeRawPtr<ScriptPromiseResolver> resolver = ScriptPromiseResolver::create(scriptState);
     ScriptPromise promise = resolver->promise();
 
-    ExecutionContext* executionContext = scriptState->executionContext();
     ServiceWorkerGlobalScopeClient::from(executionContext)->skipWaiting(new SkipWaitingCallback(resolver));
     return promise;
 }
 
 bool ServiceWorkerGlobalScope::addEventListener(const AtomicString& eventType, PassRefPtr<EventListener> listener, bool useCapture)
 {
     if (m_didEvaluateScript) {
         if (eventType == EventTypeNames::install) {
             RefPtrWillBeRawPtr<ConsoleMessage> consoleMessage = ConsoleMessage::create(JSMessageSource, WarningMessageLevel, "Event handler of 'install' event must be added on the initial evaluation of worker script.");
             addMessageToWorkerConsole(consoleMessage.release());
@@ skipping 50 matching lines @@
 void ServiceWorkerGlobalScope::logExceptionToConsole(const String& errorMessage, int scriptId, const String& sourceURL, int lineNumber, int columnNumber, PassRefPtrWillBeRawPtr<ScriptCallStack> callStack)
 {
     WorkerGlobalScope::logExceptionToConsole(errorMessage, scriptId, sourceURL, lineNumber, columnNumber, callStack);
     RefPtrWillBeRawPtr<ConsoleMessage> consoleMessage = ConsoleMessage::create(JSMessageSource, ErrorMessageLevel, errorMessage, sourceURL, lineNumber);
     consoleMessage->setScriptId(scriptId);
     consoleMessage->setCallStack(callStack);
     addMessageToWorkerConsole(consoleMessage.release());
 }
 
 } // namespace blink