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

chrome/browser/sync/engine/verify_updates_command_unittest.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 "base/location.h"
 #include "chrome/browser/sync/engine/verify_updates_command.h"
 #include "chrome/browser/sync/protocol/bookmark_specifics.pb.h"
+#include "chrome/browser/sync/sessions/session_state.h"
 #include "chrome/browser/sync/sessions/sync_session.h"
 #include "chrome/browser/sync/syncable/directory_manager.h"
 #include "chrome/browser/sync/syncable/syncable.h"
 #include "chrome/browser/sync/syncable/syncable_id.h"
 #include "chrome/browser/sync/test/engine/fake_model_worker.h"
 #include "chrome/browser/sync/test/engine/syncer_command_test.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace browser_sync {
 
@@ skipping 56 matching lines @@
 };
 
 TEST_F(VerifyUpdatesCommandTest, AllVerified) {
   string root = syncable::GetNullId().GetServerId();
 
   CreateLocalItem("b1", root, syncable::BOOKMARKS);
   CreateLocalItem("b2", root, syncable::BOOKMARKS);
   CreateLocalItem("p1", root, syncable::PREFERENCES);
   CreateLocalItem("a1", root, syncable::AUTOFILL);
 
+  ExpectNoGroupsToChange(command_);
+
   GetUpdatesResponse* updates = session()->mutable_status_controller()->
       mutable_updates_response()->mutable_get_updates();
   AddUpdate(updates, "b1", root, syncable::BOOKMARKS);
   AddUpdate(updates, "b2", root, syncable::BOOKMARKS);
   AddUpdate(updates, "p1", root, syncable::PREFERENCES);
   AddUpdate(updates, "a1", root, syncable::AUTOFILL);
 
+  ExpectGroupsToChange(command_, GROUP_UI, GROUP_DB);
+
   command_.ExecuteImpl(session());
 
   StatusController* status = session()->mutable_status_controller();
   {
     sessions::ScopedModelSafeGroupRestriction r(status, GROUP_UI);
     ASSERT_TRUE(status->update_progress());
     EXPECT_EQ(3, status->update_progress()->VerifiedUpdatesSize());
   }
   {
     sessions::ScopedModelSafeGroupRestriction r(status, GROUP_DB);
     ASSERT_TRUE(status->update_progress());
     EXPECT_EQ(1, status->update_progress()->VerifiedUpdatesSize());
   }
   {
     sessions::ScopedModelSafeGroupRestriction r(status, GROUP_PASSIVE);
     EXPECT_FALSE(status->update_progress());
   }
 }
 
 }