Fix crash when an extension popup shows a JS alert. Showing the alert takes...

chrome/browser/jsmessage_box_client.h

 // Copyright (c) 2009 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_JSMESSAGE_BOX_CLIENT_H_
 #define CHROME_BROWSER_JSMESSAGE_BOX_CLIENT_H_
 
 // JavaScriptMessageBoxClient
 //
 // An interface implemented by an object that receives results from JavaScript
 // message boxes (alert, confirm, and prompt).
 //
 
 #include <string>
 
 #include "app/gfx/native_widget_types.h"
 
+class ExtensionHost;
 class GURL;
 class Profile;
 class TabContents;
 namespace IPC {
 class Message;
 }
 
 class JavaScriptMessageBoxClient {
  public:
   virtual ~JavaScriptMessageBoxClient() {}
 
   // Returns the title to use for the message box.
   virtual std::wstring GetMessageBoxTitle(const GURL& frame_url,
                                           bool is_alert) = 0;
 
   // Returns the root native window with which the message box is associated.
   virtual gfx::NativeWindow GetMessageBoxRootWindow() = 0;
 
   // AppModalDialog calls this when the dialog is closed.
   virtual void OnMessageBoxClosed(IPC::Message* reply_msg,
                                   bool success,
                                   const std::wstring& prompt) = 0;
 
   // Indicates whether additional message boxes should be suppressed.
   virtual void SetSuppressMessageBoxes(bool suppress_message_boxes) = 0;
 
-  // Returns the TabContents associated with this message box -- in practice,
-  // the TabContents implementing this interface -- or NULL if it has no
-  // TabContents (e.g., it's an ExtensionHost).
+  // Returns the TabContents or ExtensionHost associated with this message
+  // box -- in practice, the object implementing this interface. Exactly one of
+  // these must be non-NULL; behavior is undefined (read: it'll probably crash)
+  // if that is not the case.
   virtual TabContents* AsTabContents() = 0;
+  virtual ExtensionHost* AsExtensionHost() = 0;
 };
 
 #endif  // CHROME_BROWSER_JSMESSAGE_BOX_CLIENT_H_