Allow app_shell embedders to override extensions client interfaces

extensions/shell/renderer/shell_content_renderer_client.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 "extensions/shell/renderer/shell_content_renderer_client.h"
 
 #include "content/public/common/content_constants.h"
 #include "content/public/renderer/render_frame.h"
 #include "content/public/renderer/render_frame_observer.h"
 #include "content/public/renderer/render_frame_observer_tracker.h"
@@ skipping 61 matching lines @@
 
 ShellContentRendererClient::ShellContentRendererClient() {
 }
 
 ShellContentRendererClient::~ShellContentRendererClient() {
 }
 
 void ShellContentRendererClient::RenderThreadStarted() {
   RenderThread* thread = RenderThread::Get();
 
-  extensions_client_.reset(new ShellExtensionsClient);
+  extensions_client_.reset(CreateExtensionsClient());
   ExtensionsClient::Set(extensions_client_.get());
 
   extensions_renderer_client_.reset(new ShellExtensionsRendererClient);
   ExtensionsRendererClient::Set(extensions_renderer_client_.get());
 
   extension_dispatcher_delegate_.reset(new DefaultDispatcherDelegate());
 
   // Must be initialized after ExtensionsRendererClient.
   extension_dispatcher_.reset(
       new Dispatcher(extension_dispatcher_delegate_.get()));
@@ skipping 89 matching lines @@
     const std::string& mime_type,
     const GURL& original_url) {
   if (mime_type == content::kBrowserPluginMimeType) {
     return new extensions::ExtensionsGuestViewContainer(render_frame);
   } else {
     return new extensions::MimeHandlerViewContainer(
         render_frame, mime_type, original_url);
   }
 }
 
+ExtensionsClient* ShellContentRendererClient::CreateExtensionsClient() {
+  return new ShellExtensionsClient;
+}
+
 }  // namespace extensions