Cleanup: Add more conversion helpers for usage.

Source/web/WebDataSourceImpl.h

 /*
  * 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 73 matching lines @@
     // Mutable because the const getters will magically sync these to the
     // latest version from WebKit.
     mutable WrappedResourceRequest m_originalRequestWrapper;
     mutable WrappedResourceRequest m_requestWrapper;
     mutable WrappedResourceResponse m_responseWrapper;
 
     OwnPtr<ExtraData> m_extraData;
     OwnPtr<WebPluginLoadObserver> m_pluginLoadObserver;
 };
 
+inline WebDataSourceImpl* toWebDataSourceImpl(WebDataSource* source)
+{
+    ASSERT_WITH_SECURITY_IMPLICATION(!source);

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

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

+    return static_cast<WebDataSourceImpl*>(source);
+}
+
 } // namespace WebKit
 
 #endif  // WebDataSourceImpl_h