Make the id used in IconMsg_DownloadFavicon unique

chrome/browser/favicon/favicon_handler_delegate.h

 // Copyright (c) 2011 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_FAVICON_FAVICON_HANDLER_DELEGATE_H_
 #define CHROME_BROWSER_FAVICON_FAVICON_HANDLER_DELEGATE_H_
 #pragma once
 
 class GURL;
 
 namespace content {
 class NavigationEntry;
 }
 
 // This class provides a delegate interface for a FaviconHandler.  It allows the
 // FaviconHandler to ask its delegate for information or notify its delegate
 // about changes.
 class FaviconHandlerDelegate {
  public:
   // Returns the current NavigationEntry.
   virtual content::NavigationEntry* GetActiveEntry() = 0;
 
-  // Starts the download for the given favicon.  When finished, the delegate
-  // will call |OnDidDownloadFavicon()| with the results.
-  virtual void StartDownload(int id, const GURL& url, int image_size) = 0;
+  // Starts the download for the given favicon. When finished, the delegate
+  // will call OnDidDownloadFavicon() with the results.
+  // Returns the unique id of the download request. The id will be passed
+  // in OnDidDownloadFavicon().
+  virtual int StartDownload(const GURL& url, int image_size) = 0;
 
   // Notifies the delegate that the favicon for the active entry was updated.
   virtual void NotifyFaviconUpdated() = 0;
 };
 
 #endif  // CHROME_BROWSER_FAVICON_FAVICON_HANDLER_DELEGATE_H_