sync: Add pre-commit update avoidance mode + flag

sync/test/engine/syncer_command_test.h

 // 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.
 
 #ifndef SYNC_TEST_ENGINE_SYNCER_COMMAND_TEST_H_
 #define SYNC_TEST_ENGINE_SYNCER_COMMAND_TEST_H_
 
 #include <algorithm>
 #include <string>
 #include <vector>
@@ skipping 118 matching lines @@
   }
 
   void ResetContext() {
     context_.reset(new sessions::SyncSessionContext(
             mock_server_.get(), directory(),
             GetWorkers(), &extensions_activity_monitor_,
             std::vector<SyncEngineEventListener*>(),
             &mock_debug_info_getter_,
             &traffic_recorder_,
             true,  // enable keystore encryption
+            false,  // force enable pre-commit GU avoidance experiment
             "fake_invalidator_client_id"));
     context_->set_routing_info(routing_info_);
     context_->set_account_name(directory()->name());
     ClearSession();
   }
 
   // Install a MockServerConnection.  Resets the context.  By default,
   // the context does not have a MockServerConnection attached.
   void ConfigureMockServerConnection() {
     mock_server_.reset(new MockConnectionManager(directory()));
@@ skipping 71 matching lines @@
   virtual void TearDown() OVERRIDE;
   virtual syncable::Directory* directory() OVERRIDE;
 
  private:
   TestDirectorySetterUpper dir_maker_;
 };
 
 }  // namespace syncer
 
 #endif  // SYNC_TEST_ENGINE_SYNCER_COMMAND_TEST_H_