Make the UI an observer of downloads.

chrome/browser/prerender/prerender_contents.cc

 // Copyright (c) 2012 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.
 
 #include "chrome/browser/prerender/prerender_contents.h"
 
 #include <algorithm>
 #include <functional>
 #include <utility>
 
@@ skipping 67 matching lines @@
   }
 
   virtual bool CanDownload(RenderViewHost* render_view_host,
                            int request_id,
                            const std::string& request_method) OVERRIDE {
     prerender_contents_->Destroy(FINAL_STATUS_DOWNLOAD);
     // Cancel the download.
     return false;
   }
 
-  virtual void OnStartDownload(WebContents* source,
-                               DownloadItem* download) OVERRIDE {
-    // Prerendered pages should never be able to download files.
-    NOTREACHED();
-  }
-
   virtual bool ShouldCreateWebContents(
       WebContents* web_contents,
       int route_id,
       WindowContainerType window_container_type,
       const string16& frame_name,
       const GURL& target_url) OVERRIDE {
     // Since we don't want to permit child windows that would have a
     // window.opener property, terminate prerendering.
     prerender_contents_->Destroy(FINAL_STATUS_CREATE_NEW_WINDOW);
     // Cancel the popup.
@@ skipping 582 matching lines @@
 
 bool PrerenderContents::IsCrossSiteNavigationPending() const {
   if (!prerender_contents_)
     return false;
   return (prerender_contents_->GetSiteInstance() !=
           prerender_contents_->GetPendingSiteInstance());
 }
 
 
 }  // namespace prerender