Improve error messaging of webRequest API in case of conflicts

chrome/browser/extensions/test_extension_system.cc

 // Copyright (c) 2012 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 "chrome/browser/extensions/test_extension_system.h"
 
 #include "base/command_line.h"
 #include "chrome/browser/extensions/api/alarms/alarm_manager.h"
 #include "chrome/browser/extensions/api/messaging/message_service.h"
 #include "chrome/browser/extensions/event_router.h"
@@ skipping 150 matching lines @@
 
 ApiResourceManager<Socket>*TestExtensionSystem::socket_manager() {
   return socket_manager_.get();
 }
 
 ApiResourceManager<UsbDeviceResource>*
 TestExtensionSystem::usb_device_resource_manager() {
   return NULL;
 }
 
+ExtensionWarningService* TestExtensionSystem::warning_service() {
+  return NULL;
+}
+
 // static
 ProfileKeyedService* TestExtensionSystem::Build(Profile* profile) {
   return new TestExtensionSystem(profile);
 }
 
 }  // namespace extensions