Add null check in ChromeClientImpl::postAccessibilityNotification() for SharedWorker refactoring.

Source/web/ChromeClientImpl.cpp

 /*
  * Copyright (C) 2009 Google Inc. All rights reserved.
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies).
  *
  * 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.
@@ skipping 759 matching lines @@
     info->selectedIndex = popupContainer->selectedIndex();
     info->items.swap(outputItems);
     info->rightAligned = popupContainer->menuStyle().textDirection() == RTL;
 }
 
 void ChromeClientImpl::postAccessibilityNotification(AXObject* obj, AXObjectCache::AXNotification notification)
 {
     // Alert assistive technology about the accessibility object notification.
     if (!obj)
         return;
-
-    m_webView->client()->postAccessibilityEvent(WebAXObject(obj), toWebAXEvent(notification));
+    if (m_webView->client())
+        m_webView->client()->postAccessibilityEvent(WebAXObject(obj), toWebAXEvent(notification));
 }
 
 String ChromeClientImpl::acceptLanguages()
 {
     return m_webView->client()->acceptLanguages();
 }
 
 bool ChromeClientImpl::paintCustomOverhangArea(GraphicsContext* context, const IntRect& horizontalOverhangArea, const IntRect& verticalOverhangArea, const IntRect& dirtyRect)
 {
     Frame* frame = m_webView->mainFrameImpl()->frame();
@@ skipping 244 matching lines @@
     notImplemented();
     return NavigatorContentUtilsClient::CustomHandlersDeclined;
 }
 
 void NavigatorContentUtilsClientImpl::unregisterProtocolHandler(const String& scheme, const String& baseURL, const String& url)
 {
     notImplemented();
 }
 
 } // namespace blink