Make BackgroundContentsService start up BackgroundContents with a delay, as for ExtensionHosts.

extensions/shell/browser/shell_extension_host_delegate.h

 // 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.
 
 #ifndef EXTENSIONS_SHELL_BROWSER_SHELL_EXTENSION_HOST_DELEGATE_H_
 #define EXTENSIONS_SHELL_BROWSER_SHELL_EXTENSION_HOST_DELEGATE_H_
 
 #include "base/macros.h"
 #include "extensions/browser/extension_host_delegate.h"
 
@@ skipping 15 matching lines @@
                  const gfx::Rect& initial_rect,
                  bool user_gesture) override;
   void ProcessMediaAccessRequest(content::WebContents* web_contents,
                                  const content::MediaStreamRequest& request,
                                  const content::MediaResponseCallback& callback,
                                  const Extension* extension) override;
   bool CheckMediaAccessPermission(content::WebContents* web_contents,
                                   const GURL& security_origin,
                                   content::MediaStreamType type,
                                   const Extension* extension) override;
+  ExtensionHostQueue* GetExtensionHostQueue() const override;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(ShellExtensionHostDelegate);
 };
 
 }  // namespace extensions
 
 #endif  // EXTENSIONS_SHELL_BROWSER_SHELL_EXTENSION_HOST_DELEGATE_H_