Implement sidebar support for extension action popups

extensions/browser/extension_system.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/browser/extension_system.h"
 
 #include "components/keyed_service/content/browser_context_keyed_service_factory.h"
 #include "extensions/browser/extension_system_provider.h"
 #include "extensions/browser/extensions_browser_client.h"
 
 namespace extensions {
 
 ExtensionSystem::ExtensionSystem() {
 }
 
 ExtensionSystem::~ExtensionSystem() {
 }
 
 // static
 ExtensionSystem* ExtensionSystem::Get(content::BrowserContext* context) {
   return ExtensionsBrowserClient::Get()
       ->GetExtensionSystemFactory()
       ->GetForBrowserContext(context);
 }
 
+SidebarManager* ExtensionSystem::sidebar_manager() {
+  return nullptr;
+}
+
 }  // namespace extensions