app_shell: Fix PrefsTabHelper dependency of ExtensionHost

apps/shell/shell_extensions_browser_client.cc

 // 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 "apps/shell/shell_extensions_browser_client.h"
 
 #include "apps/shell/shell_app_sorting.h"
 #include "base/prefs/pref_service.h"
 #include "base/prefs/pref_service_factory.h"
 #include "base/prefs/testing_pref_store.h"
@@ skipping 78 matching lines @@
 bool ShellExtensionsBrowserClient::DeferLoadingBackgroundHosts(
     BrowserContext* context) const {
   return false;
 }
 
 bool ShellExtensionsBrowserClient::IsBackgroundPageAllowed(
     BrowserContext* context) const {
   return true;
 }
 
+void ShellExtensionsBrowserClient::OnExtensionHostCreated(
+    content::WebContents* web_contents) {
+}
+
 bool ShellExtensionsBrowserClient::DidVersionUpdate(BrowserContext* context) {
   // TODO(jamescook): We might want to tell extensions when app_shell updates.
   return false;
 }
 
 scoped_ptr<extensions::AppSorting>
 ShellExtensionsBrowserClient::CreateAppSorting() {
   return scoped_ptr<extensions::AppSorting>(new ShellAppSorting).Pass();
 }
 
 bool ShellExtensionsBrowserClient::IsRunningInForcedAppMode() {
   return false;
 }
 
 content::JavaScriptDialogManager*
 ShellExtensionsBrowserClient::GetJavaScriptDialogManager() {
   // TODO(jamescook): Create a JavaScriptDialogManager or reuse the one from
   // content_shell.
   NOTREACHED();
   return NULL;
 }
 
 }  // namespace apps