Cleanup: Add conversion interface for WebWidget derived classes.

Source/web/WebPagePopupImpl.h

 /*
  * 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:
  *
  *     * 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 55 matching lines @@
 private:
     // WebWidget functions
     virtual WebSize size() OVERRIDE;
     virtual void animate(double) OVERRIDE;
     virtual void layout() OVERRIDE;
     virtual void paint(WebCanvas*, const WebRect&, PaintOptions = ReadbackFromCompositorIfAvailable) OVERRIDE;
     virtual void resize(const WebSize&) OVERRIDE;
     virtual void close() OVERRIDE;
     virtual bool handleInputEvent(const WebInputEvent&) OVERRIDE;
     virtual void setFocus(bool) OVERRIDE;
+    virtual bool isPagePopup() const OVERRIDE { return true; }
 
     // PageWidgetEventHandler functions
     virtual bool handleKeyEvent(const WebKeyboardEvent&) OVERRIDE;
     virtual bool handleCharEvent(const WebKeyboardEvent&) OVERRIDE;
     virtual bool handleGestureEvent(const WebGestureEvent&) OVERRIDE;
 
     explicit WebPagePopupImpl(WebWidgetClient*);
     bool initializePage();
     void destroyPage();
 
     WebWidgetClient* m_widgetClient;
     WebRect m_windowRectInScreen;
     WebViewImpl* m_webView;
     OwnPtr<WebCore::Page> m_page;
     OwnPtr<PagePopupChromeClient> m_chromeClient;
     WebCore::PagePopupClient* m_popupClient;
     bool m_closing;
 
     friend class WebPagePopup;
     friend class PagePopupChromeClient;
 };
 
+inline WebPagePopupImpl* toWebPagePopupImpl(WebWidget* widget)
+{
+    ASSERT_WITH_SECURITY_IMPLICATION(!widget || widget->isPagePopup());
+    return static_cast<WebPagePopupImpl*>(widget);
+}
+
+inline WebPagePopupImpl* toWebPagePopupImpl(WebCore::PagePopup* popup)
+{
+    // WebPagePopupImpl is the only implementation of WebCore::PagePopup, so
+    // no further checking required.
+    return static_cast<WebPagePopupImpl*>(popup);
+}
+
 } // namespace WebKit
 #endif // WebPagePopupImpl_h