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

chrome/browser/sync/engine/verify_updates_command_unittest.cc

Index: chrome/browser/sync/engine/verify_updates_command_unittest.cc
diff --git a/chrome/browser/sync/engine/verify_updates_command_unittest.cc b/chrome/browser/sync/engine/verify_updates_command_unittest.cc
index 20aab0172454695e0d5aa7f95a1c876857c93803..7de5cf2d7785bae8faba241896cf278b9b52b532 100644
--- a/chrome/browser/sync/engine/verify_updates_command_unittest.cc
+++ b/chrome/browser/sync/engine/verify_updates_command_unittest.cc
@@ -5,6 +5,7 @@
 #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"
@@ -81,6 +82,8 @@ TEST_F(VerifyUpdatesCommandTest, AllVerified) {
   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);
@@ -88,6 +91,8 @@ TEST_F(VerifyUpdatesCommandTest, AllVerified) {
   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();