sync: Add pre-commit update avoidance mode + flag

chrome/browser/sync/glue/sync_backend_host.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/sync/glue/sync_backend_host.h"
 
 #include <algorithm>
 #include <map>
 
 #include "base/bind.h"
@@ skipping 365 matching lines @@
   InternalComponentsFactory::Switches factory_switches = {
       InternalComponentsFactory::ENCRYPTION_KEYSTORE,
       InternalComponentsFactory::BACKOFF_NORMAL
   };
 
   CommandLine* cl = CommandLine::ForCurrentProcess();
   if (cl->HasSwitch(switches::kSyncShortInitialRetryOverride)) {
     factory_switches.backoff_override =
         InternalComponentsFactoryImpl::BACKOFF_SHORT_INITIAL_RETRY_OVERRIDE;
   }
+  if (cl->HasSwitch(switches::kSyncEnableGetUpdateAvoidance)) {
+    factory_switches.pre_commit_updates_policy =
+        InternalComponentsFactoryImpl::FORCE_ENABLE_PRE_COMMIT_UPDATE_AVOIDANCE;
+  }
 
   initialization_state_ = CREATING_SYNC_MANAGER;
   InitCore(DoInitializeOptions(
       sync_thread_.message_loop(),
       registrar_.get(),
       routing_info,
       workers,
       &extensions_activity_monitor_,
       event_handler,
       sync_service_url,
@@ skipping 1231 matching lines @@
   DVLOG(1) << "Connection status changed: "
            << syncer::ConnectionStatusToString(status);
   frontend_->OnConnectionStatusChange(status);
 }
 
 #undef SDVLOG
 
 #undef SLOG
 
 }  // namespace browser_sync