Refactoring: Add toWebFrameImpl() interface.

Source/web/tests/RenderTableCellTest.cpp

 /*
  * Copyright (C) 2011 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:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 32 matching lines @@
 namespace {
 
 class RenderTableCellDeathTest : public testing::Test {
     // It's unfortunate that we have to get the whole browser stack to test one RenderObject
     // but the code needs it.
     static Frame* frame()
     {
         static WebView* webView;
 
         if (webView)
-            return static_cast<WebFrameImpl*>(webView->mainFrame())->frame();
+            return toWebFrameImpl(webView->mainFrame())->frame();
 
         webView = FrameTestHelpers::createWebViewAndLoad("about:blank");
         webView->setFocus(true);
-        return static_cast<WebFrameImpl*>(webView->mainFrame())->frame();
+        return toWebFrameImpl(webView->mainFrame())->frame();
     }
 
     static Document* document()
     {
         return frame()->document();
     }
 
     virtual void SetUp()
     {
         m_cell = RenderTableCell::createAnonymous(document());
@@ skipping 33 matching lines @@
 TEST_F(RenderTableCellDeathTest, CrashIfSettingUnsetColumnIndex)
 {
     ASSERT_DEATH(m_cell->setCol(unsetColumnIndex), "");
 }
 
 #endif
 
 }
 
 } // namespace WebCore