[sync] skeleton implementation of TypedURLSyncBridge

chrome/browser/sync/chrome_sync_client.cc

 // Copyright 2015 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/sync/chrome_sync_client.h"
 
 #include <utility>
 
 #include "base/bind.h"
 #include "base/command_line.h"
@@ skipping 438 matching lines @@
       return base::WeakPtr<syncer::ModelTypeSyncBridge>();
     case syncer::AUTOFILL:
       return autofill::AutocompleteSyncBridge::FromWebDataService(
           web_data_service_.get());
 #if defined(OS_CHROMEOS)
     case syncer::PRINTERS:
       return chromeos::PrintersManagerFactory::GetForBrowserContext(profile_)
           ->GetSyncBridge()
           ->AsWeakPtr();
 #endif
+    case syncer::TYPED_URLS: {
+      // We request history service with explicit access here because this
+      // codepath is executed on backend thread while HistoryServiceFactory

[skym, 2017/03/03 17:41:09]

I'm not sure I agree with you that the way the code is currently set up in this
CL, will actually call this on anything other than the UI thread.

[Gang Wu, 2017/03/06 08:21:23]

Done.

+      // checks preference value in implicit mode and PrefService expectes calls
+      // only from UI thread.
+      history::HistoryService* history = HistoryServiceFactory::GetForProfile(
+          profile_, ServiceAccessType::EXPLICIT_ACCESS);
+      if (!history)
+        return base::WeakPtr<history::TypedURLSyncBridge>();
+      return history->GetTypedURLSyncBridge()->AsWeakPtr();
+    }
     default:
       NOTREACHED();
       return base::WeakPtr<syncer::ModelTypeSyncBridge>();
   }
 }
 
 scoped_refptr<syncer::ModelSafeWorker>
 ChromeSyncClient::CreateModelWorkerForGroup(syncer::ModelSafeGroup group) {
   DCHECK_CURRENTLY_ON(BrowserThread::UI);
   switch (group) {
@@ skipping 183 matching lines @@
   sync_service->RegisterDataTypeController(
       base::MakeUnique<SupervisedUserSyncDataTypeController>(
           syncer::SUPERVISED_USER_SETTINGS, error_callback, this, profile_));
   sync_service->RegisterDataTypeController(
       base::MakeUnique<SupervisedUserSyncDataTypeController>(
           syncer::SUPERVISED_USER_WHITELISTS, error_callback, this, profile_));
 #endif
 }
 
 }  // namespace browser_sync