Cleanup: Add more conversion helpers for usage.

Source/web/WebDevToolsAgentImpl.h

 /*
  * Copyright (C) 2010 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 118 matching lines @@
     WebCore::InspectorController* inspectorController();
     WebCore::Frame* mainFrame();
 
     int m_hostId;
     WebDevToolsAgentClient* m_client;
     WebViewImpl* m_webViewImpl;
     bool m_attached;
     OwnPtr<DeviceMetricsSupport> m_metricsSupport;
 };
 
+inline WebDevToolsAgentImpl* toWebDevToolsAgentImpl(WebDevToolsAgent* agent)
+{
+    ASSERT_WITH_SECURITY_IMPLICATION(!agent);

[tkent, 2013/10/08 05:24:04]

Null pointer has no security implication.
Please do not reject null agent for consistency.

+    return static_cast<WebDevToolsAgentImpl*>(agent);
+}
+
 } // namespace WebKit
 
 #endif