Cleanup: Add more conversion helpers for usage.

Source/web/ChromeClientImpl.h

 /*
  * 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 199 matching lines @@
 
     virtual void registerProtocolHandler(const String& scheme, const String& baseURL, const String& url, const String& title) OVERRIDE;
 
 private:
     explicit NavigatorContentUtilsClientImpl(WebViewImpl*);
 
     WebViewImpl* m_webView;
 };
 #endif
 
+inline ChromeClientImpl* toChromeClientImpl(WebCore::ChromeClient* client)
+{
+    // 1. The client returned by Page::client() is a reference, hence never null.
+    // 2. There is no other class derived from ChromeClient other than ChromeClientImpl.

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

It's incorrect. AFAIK, we have EmptyChromeClient, PagePopupChromeClient,
HelperPluginChromeClient.

+    // Hence, we don't need ASSERT here to check for either of the conditions.
+    return static_cast<ChromeClientImpl*>(client);
+}
+
 } // namespace WebKit
 
 #endif