Refactoring: Add toWebFrameImpl() interface.

Source/web/WebPageSerializer.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 221 matching lines @@
 {
     WebPageSerializerImpl serializerImpl(
         frame, recursive, client, links, localPaths, localDirectoryName);
     return serializerImpl.serialize();
 }
 
 bool WebPageSerializer::retrieveAllResources(WebView* view,
                                              const WebVector<WebCString>& supportedSchemes,
                                              WebVector<WebURL>* resourceURLs,
                                              WebVector<WebURL>* frameURLs) {
-    WebFrameImpl* mainFrame = static_cast<WebFrameImpl*>(view->mainFrame());
+    WebFrameImpl* mainFrame = toWebFrameImpl(view->mainFrame());
     if (!mainFrame)
         return false;
 
     Vector<Frame*> framesToVisit;
     Vector<Frame*> visitedFrames;
     Vector<KURL> frameKURLs;
     Vector<KURL> resourceKURLs;
 
     // Let's retrieve the resources from every frame in this page.
     framesToVisit.append(mainFrame->frame());
@@ skipping 39 matching lines @@
 
 WebString WebPageSerializer::generateBaseTagDeclaration(const WebString& baseTarget)
 {
     if (baseTarget.isEmpty())
         return String("<base href=\".\">");
     String baseString = "<base href=\".\" target=\"" + static_cast<const String&>(baseTarget) + "\">";
     return baseString;
 }
 
 } // namespace WebKit