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

chrome/browser/sync/engine/process_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/basictypes.h"
+#include "base/memory/ref_counted.h"
+#include "chrome/browser/sync/engine/process_updates_command.h"
+#include "chrome/browser/sync/sessions/session_state.h"
+#include "chrome/browser/sync/sessions/sync_session.h"
+#include "chrome/browser/sync/syncable/model_type.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 {
+
+namespace {
+
+class ProcessUpdatesCommandTest : public SyncerCommandTest {
+ protected:
+  ProcessUpdatesCommandTest() {}
+  virtual ~ProcessUpdatesCommandTest() {}
+
+  virtual void SetUp() {
+    workers()->push_back(
+        make_scoped_refptr(new FakeModelWorker(GROUP_UI)));
+    workers()->push_back(
+        make_scoped_refptr(new FakeModelWorker(GROUP_DB)));
+    (*mutable_routing_info())[syncable::BOOKMARKS] = GROUP_UI;
+    (*mutable_routing_info())[syncable::AUTOFILL] = GROUP_DB;
+    SyncerCommandTest::SetUp();
+  }
+
+  ProcessUpdatesCommand command_;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(ProcessUpdatesCommandTest);
+};
+
+TEST_F(ProcessUpdatesCommandTest, GetGroupsToChange) {
+  ExpectNoGroupsToChange(command_);
+  // Add a verified update for GROUP_DB.
+  session()->mutable_status_controller()->
+      GetUnrestrictedMutableUpdateProgressForTest(GROUP_DB)->
+      AddVerifyResult(VerifyResult(), sync_pb::SyncEntity());
+  ExpectGroupToChange(command_, GROUP_DB);
+}
+
+}  // namespace
+
+}  // namespace browser_sync