Refactoring: Add convenience method toPluginContainerImpl.

Source/web/WebPluginScrollbarImpl.cpp

 /*
  * Copyright (C) 2012 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
  *     notice, this list of conditions and the following disclaimer in the
@@ skipping 32 matching lines @@
 
 using namespace std;
 using namespace WebCore;
 
 namespace WebKit {
 
 WebPluginScrollbar* WebPluginScrollbar::createForPlugin(Orientation orientation,
                                                         WebPluginContainer* pluginContainer,
                                                         WebPluginScrollbarClient* client)
 {
-    WebPluginContainerImpl* plugin = static_cast<WebPluginContainerImpl*>(pluginContainer);
+    WebPluginContainerImpl* plugin = toPluginContainerImpl(pluginContainer);
     return new WebPluginScrollbarImpl(orientation, plugin->scrollbarGroup(), client);
 }
 
 int WebPluginScrollbar::defaultThickness()
 {
     return ScrollbarTheme::theme()->scrollbarThickness();
 }
 
 WebPluginScrollbarImpl::WebPluginScrollbarImpl(Orientation orientation,
                                    ScrollbarGroup* group,
@@ skipping 301 matching lines @@
     WebCore::ScrollDirection scrollDirection;
     WebCore::ScrollGranularity scrollGranularity;
     if (WebViewImpl::mapKeyCodeForScroll(keyCode, &scrollDirection, &scrollGranularity)) {
         // Will return false if scroll direction wasn't compatible with this scrollbar.
         return m_group->scroll(scrollDirection, scrollGranularity);
     }
     return false;
 }
 
 } // namespace WebKit