Add the main frame routing ID to WebContentsDelegate, use it in BackgroundContents.

content/shell/browser/shell_web_contents_view_delegate_mac.mm

 // 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.
 
 #include "content/shell/browser/shell_web_contents_view_delegate.h"
 
 #import  <Cocoa/Cocoa.h>
 
 #include "base/command_line.h"
 #include "content/public/browser/render_frame_host.h"
@@ skipping 223 matching lines @@
       break;
     case ShellContextMenuItemDeleteTag:
       web_contents_->Delete();
       break;
     case ShellContextMenuItemOpenLinkTag: {
       ShellBrowserContext* browser_context =
           ShellContentBrowserClient::Get()->browser_context();
       Shell::CreateNewWindow(browser_context,
                              params_.link_url,
                              NULL,
-                             MSG_ROUTING_NONE,
                              gfx::Size());
       break;
     }
     case ShellContextMenuItemBackTag:
       web_contents_->GetController().GoToOffset(-1);
       web_contents_->Focus();
       break;
     case ShellContextMenuItemForwardTag:
       web_contents_->GetController().GoToOffset(1);
       web_contents_->Focus();
       break;
     case ShellContextMenuItemReloadTag: {
       web_contents_->GetController().Reload(false);
       web_contents_->Focus();
       break;
     }
     case ShellContextMenuItemInspectTag: {
       ShellDevToolsFrontend::Show(web_contents_);
       break;
     }
   }
 }
 
 }  // namespace content