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

chrome/browser/sync/engine/build_and_process_conflict_sets_command.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/sync/engine/build_and_process_conflict_sets_command.h"
 
 #include <set>
 #include <string>
 #include <sstream>
 #include <vector>
@@ skipping 12 matching lines @@
 using sessions::StatusController;
 using sessions::SyncSession;
 using sessions::UpdateProgress;
 using std::set;
 using std::string;
 using std::vector;
 
 BuildAndProcessConflictSetsCommand::BuildAndProcessConflictSetsCommand() {}
 BuildAndProcessConflictSetsCommand::~BuildAndProcessConflictSetsCommand() {}
 
+std::set<ModelSafeGroup> BuildAndProcessConflictSetsCommand::GetGroupsToChange(
+    const sessions::SyncSession& session) const {
+  return GetActiveGroupsWithConflicts(session);
+}
+
 void BuildAndProcessConflictSetsCommand::ModelChangingExecuteImpl(
     SyncSession* session) {
   session->mutable_status_controller()->update_conflict_sets_built(
       BuildAndProcessConflictSets(session));
 }
 
 bool BuildAndProcessConflictSetsCommand::BuildAndProcessConflictSets(
     SyncSession* session) {
   syncable::ScopedDirLookup dir(session->context()->directory_manager(),
                                 session->context()->account_name());
@@ skipping 362 matching lines @@
     LocallyDeletedPathChecker checker;
     if (!checker.CausingConflict(parent, *entry))
       return;
     conflict_progress->MergeSets(entry->Get(syncable::ID),
                                  parent.Get(syncable::ID));
     CrawlDeletedTreeMergingSets(trans, parent, conflict_progress, checker);
   }
 }
 
 }  // namespace browser_sync