Refactoring: Add convenience method toPluginContainerImpl.

Source/web/WebPluginContainerImpl.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 35 matching lines @@
 class GestureEvent;
 class HTMLPlugInElement;
 class IntRect;
 class KeyboardEvent;
 class MouseEvent;
 class PlatformGestureEvent;
 class ResourceError;
 class ResourceResponse;
 class TouchEvent;
 class WheelEvent;
+class Widget;
 }
 
 namespace WebKit {
 
 struct WebPrintParams;
 
 class ScrollbarGroup;
 class WebPlugin;
 class WebPluginLoadObserver;
 class WebExternalTextureLayer;
@@ skipping 124 matching lines @@
     WebLayer* m_webLayer;
 
     // The associated scrollbar group object, created lazily. Used for Pepper
     // scrollbars.
     OwnPtr<ScrollbarGroup> m_scrollbarGroup;
 
     TouchEventRequestType m_touchEventRequestType;
     bool m_wantsWheelEvents;
 };
 
+inline WebPluginContainerImpl* toPluginContainerImpl(WebCore::Widget* widget)
+{
+    ASSERT_WITH_SECURITY_IMPLICATION(!widget || widget->isPluginContainer());
+    // We need to ensure that the object is actually of type PluginContainer
+    // as there are many subclasses of Widget.
+    return static_cast<WebPluginContainerImpl*>(widget);
+}
+
+inline WebPluginContainerImpl* toPluginContainerImpl(WebPluginContainer* container)
+{
+    // Unlike Widget, we need not worry about object type for container.
+    // WebPluginContainerImpl is the only subclass of WebPluginContainer.
+    return static_cast<WebPluginContainerImpl*>(container);
+}
+
+// This will catch anyone doing an unnecessary cast.
+void toPluginContainerImpl(const WebPluginContainerImpl*);
+
 } // namespace WebKit
 
 #endif