[Sync] Make syncer commands avoid posting tasks on threads with no work to do

chrome/browser/sync/engine/build_and_process_conflict_sets_command.h

 // 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.
 
 #ifndef CHROME_BROWSER_SYNC_ENGINE_BUILD_AND_PROCESS_CONFLICT_SETS_COMMAND_H_
 #define CHROME_BROWSER_SYNC_ENGINE_BUILD_AND_PROCESS_CONFLICT_SETS_COMMAND_H_
 #pragma once
 
 #include <vector>
 
@@ skipping 17 matching lines @@
 namespace sessions {
 class ConflictProgress;
 class StatusController;
 }
 
 class BuildAndProcessConflictSetsCommand : public ModelChangingSyncerCommand {
  public:
   BuildAndProcessConflictSetsCommand();
   virtual ~BuildAndProcessConflictSetsCommand();
 
+ protected:
   // ModelChangingSyncerCommand implementation.
+  virtual std::set<ModelSafeGroup> GetGroupsToChange(
+      const sessions::SyncSession& session) const OVERRIDE;
   virtual void ModelChangingExecuteImpl(
       sessions::SyncSession* session) OVERRIDE;
 
  private:
   bool BuildAndProcessConflictSets(sessions::SyncSession* session);
 
   bool ProcessSingleDirectionConflictSets(
       syncable::WriteTransaction* trans, ConflictResolver* resolver,
       Cryptographer* cryptographer, sessions::StatusController* status,
       const ModelSafeRoutingInfo& routes);
@@ skipping 19 matching lines @@
   void MergeSetsForPositionUpdate(syncable::BaseTransaction* trans,
       syncable::Entry* entry,
       sessions::ConflictProgress* conflict_progress);
 
   DISALLOW_COPY_AND_ASSIGN(BuildAndProcessConflictSetsCommand);
 };
 
 }  // namespace browser_sync
 
 #endif  // CHROME_BROWSER_SYNC_ENGINE_BUILD_AND_PROCESS_CONFLICT_SETS_COMMAND_H_