Enable sync for the settings from the Extension Settings API.

chrome/browser/extensions/test_extension_service.cc

 // Copyright (c) 2011 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/crx_installer.h"
 #include "chrome/browser/extensions/extension_sync_data.h"
 #include "chrome/browser/extensions/test_extension_service.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 TestExtensionService::~TestExtensionService() {}
 
+const std::vector<std::string> TestExtensionService::GetAllExtensionIds(
+    ) const {
+  ADD_FAILURE();
+  return std::vector<std::string>();
+}
+
 const ExtensionList* TestExtensionService::extensions() const {
   ADD_FAILURE();
   return NULL;
 }
 
 PendingExtensionManager* TestExtensionService::pending_extension_manager() {
   ADD_FAILURE();
   return NULL;
 }
 
@@ skipping 60 matching lines @@
   ADD_FAILURE();
   return SyncDataList();
 }
 
 SyncError TestExtensionService::ProcessSyncChanges(
     const tracked_objects::Location& from_here,
     const SyncChangeList& change_list) {
   ADD_FAILURE();
   return SyncError();
 }