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

content/shell/browser/layout_test/layout_test_devtools_frontend.cc

 // Copyright 2014 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/layout_test/layout_test_devtools_frontend.h"
 
 #include "base/command_line.h"
 #include "base/path_service.h"
 #include "base/strings/stringprintf.h"
 #include "content/public/browser/web_contents.h"
 #include "content/shell/browser/shell.h"
 #include "content/shell/browser/webkit_test_controller.h"
 #include "net/base/filename_util.h"
 
 namespace content {
 
 // static
 LayoutTestDevToolsFrontend* LayoutTestDevToolsFrontend::Show(
     WebContents* inspected_contents,
     const std::string& settings,
     const std::string& frontend_url) {
   scoped_refptr<DevToolsAgentHost> agent(
       DevToolsAgentHost::GetOrCreateFor(inspected_contents));
   Shell* shell = Shell::CreateNewWindow(inspected_contents->GetBrowserContext(),
                                         GURL(),
                                         NULL,
-                                        MSG_ROUTING_NONE,
                                         gfx::Size());
   LayoutTestDevToolsFrontend* devtools_frontend =
       new LayoutTestDevToolsFrontend(shell, agent.get());
 
   shell->LoadURL(GetDevToolsPathAsURL(settings, frontend_url));
 
   return devtools_frontend;
 }
 
 LayoutTestDevToolsFrontend::LayoutTestDevToolsFrontend(
@@ skipping 32 matching lines @@
                                      settings.c_str()));
   return result;
 }
 
 void LayoutTestDevToolsFrontend::RenderProcessGone(
     base::TerminationStatus status) {
   WebKitTestController::Get()->DevToolsProcessCrashed();
 }
 
 }  // namespace content