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

chrome/browser/sync/engine/verify_updates_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/verify_updates_command.h"
 
 #include <string>
 
 #include "base/location.h"
 #include "chrome/browser/sync/engine/syncer.h"
 #include "chrome/browser/sync/engine/syncer_proto_util.h"
 #include "chrome/browser/sync/engine/syncer_types.h"
 #include "chrome/browser/sync/engine/syncer_util.h"
 #include "chrome/browser/sync/engine/syncproto.h"
 #include "chrome/browser/sync/protocol/bookmark_specifics.pb.h"
 #include "chrome/browser/sync/syncable/directory_manager.h"
 #include "chrome/browser/sync/syncable/syncable.h"
 
 namespace browser_sync {
 
 using syncable::ScopedDirLookup;
 using syncable::WriteTransaction;
 
 using syncable::GET_BY_ID;
 using syncable::SYNCER;
 
 VerifyUpdatesCommand::VerifyUpdatesCommand() {}
 VerifyUpdatesCommand::~VerifyUpdatesCommand() {}
 
+std::set<ModelSafeGroup> VerifyUpdatesCommand::GetGroupsToChange(
+    const sessions::SyncSession& session) const {
+  std::set<ModelSafeGroup> groups_with_updates;
+
+  const GetUpdatesResponse& updates =
+      session.status_controller().updates_response().get_updates();
+  for (int i = 0; i < updates.entries().size(); i++) {
+    groups_with_updates.insert(
+        GetGroupForModelType(syncable::GetModelType(updates.entries(i)),
+                             session.routing_info()));
+  }
+
+  return groups_with_updates;
+}
+
 void VerifyUpdatesCommand::ModelChangingExecuteImpl(
     sessions::SyncSession* session) {
   VLOG(1) << "Beginning Update Verification";
   ScopedDirLookup dir(session->context()->directory_manager(),
                       session->context()->account_name());
   if (!dir.good()) {
     LOG(ERROR) << "Scoped dir lookup failed!";
     return;
   }
   WriteTransaction trans(FROM_HERE, SYNCER, dir);
@@ skipping 80 matching lines @@
         deleted, is_directory, model_type);
   }
 
   if (VERIFY_UNDECIDED == result.value)
     result.value = VERIFY_SUCCESS;  // No news is good news.
 
   return result;  // This might be VERIFY_SUCCESS as well
 }
 
 }  // namespace browser_sync