Don't create external extension providers for a TestExtensionSystem.

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 "chrome/browser/extensions/api/alarms/alarm_manager.h"
 #include "chrome/browser/extensions/extension_devtools_manager.h"
 #include "chrome/browser/extensions/extension_event_router.h"
 #include "chrome/browser/extensions/extension_info_map.h"
@@ skipping 50 matching lines @@
   state_store_.reset(new extensions::StateStore(
       profile_,
       new TestingValueStore()));
   extension_prefs_->Init(extensions_disabled);
   extension_service_.reset(new ExtensionService(profile_,
                                                 command_line,
                                                 install_directory,
                                                 extension_prefs_.get(),
                                                 autoupdate_enabled,
                                                 true));
+  extension_service_->ClearProvidersForTesting();
   return extension_service_.get();
 }
 
 extensions::ManagementPolicy* TestExtensionSystem::CreateManagementPolicy() {
   management_policy_.reset(new extensions::ManagementPolicy());
   DCHECK(extension_prefs_.get());
   management_policy_->RegisterProvider(extension_prefs_.get());
 
   return management_policy();
 }
@@ skipping 49 matching lines @@
 
 extensions::RulesRegistryService*
 TestExtensionSystem::rules_registry_service() {
   return NULL;
 }
 
 // static
 ProfileKeyedService* TestExtensionSystem::Build(Profile* profile) {
   return new TestExtensionSystem(profile);
 }