Cleanup: Add more conversion helpers for usage.

Source/web/InspectorClientImpl.cpp

 /*
  * Copyright (C) 2009 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 152 matching lines @@
 }
 
 void InspectorClientImpl::setTraceEventCallback(TraceEventCallback callback)
 {
     if (WebDevToolsAgentImpl* agent = devToolsAgent())
         agent->setTraceEventCallback(callback);
 }
 
 WebDevToolsAgentImpl* InspectorClientImpl::devToolsAgent()
 {
-    return static_cast<WebDevToolsAgentImpl*>(m_inspectedWebView->devToolsAgent());
+    return toWebDevToolsAgentImpl(m_inspectedWebView->devToolsAgent());
 }
 
 } // namespace WebKit