Refactor GuestView.

chrome/browser/guestview/guestview.h

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CHROME_BROWSER_GUESTVIEW_GUESTVIEW_H_
 #define CHROME_BROWSER_GUESTVIEW_GUESTVIEW_H_
 
 #include <queue>
 
 #include "base/memory/weak_ptr.h"
@@ skipping 64 matching lines @@
     return embedder_web_contents_;
   }
 
   // Returns the guest WebContents.
   content::WebContents* guest_web_contents() const {
     return guest_web_contents_;
   }
 
   virtual Type GetViewType() const;
 
-  // Returns a WebViewGuest if this GuestView belongs to a <webview>.
-  virtual WebViewGuest* AsWebView() = 0;
-
-  // Returns an AdViewGuest if the GuestView belongs to an <adview>.
-  virtual AdViewGuest* AsAdView() = 0;
+  // Returns a *ViewGuest if this GuestView is of the given view type.
+  template <class T>

[Xi Han, 2014/04/15 21:35:37]

We do not want a bunch of As*View functions, e.g.,AsAdView(), AsWebView() ect.
After introducing this template functions, we can obtain an *GuestView pointer
by using guest->As<*ViewGuest>() if this guest view is of the same type as the
given guest view.

+  T* As() {
+    if (GetViewType() == T::Type()) {
+      return static_cast<T*>(this);
+    }
+    return NULL;
+  }
 
   // Returns whether this guest has an associated embedder.
   bool attached() const { return !!embedder_web_contents_; }
 
   // Returns the instance ID of the <*view> element.
   int view_instance_id() const { return view_instance_id_; }
 
   // Returns the instance ID of the guest WebContents.
   int guest_instance_id() const { return guest_instance_id_; }
 
@@ skipping 41 matching lines @@
   std::queue<Event*> pending_events_;
 
   // This is used to ensure pending tasks will not fire after this object is
   // destroyed.
   base::WeakPtrFactory<GuestView> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(GuestView);
 };
 
 #endif  // CHROME_BROWSER_GUESTVIEW_GUESTVIEW_H_