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

chrome/browser/sync/engine/process_commit_response_command_unittest.cc

Index: chrome/browser/sync/engine/process_commit_response_command_unittest.cc
diff --git a/chrome/browser/sync/engine/process_commit_response_command_unittest.cc b/chrome/browser/sync/engine/process_commit_response_command_unittest.cc
index 83b8885893977df7454aa5fabb630f299b4d32d3..b22963cacb3ba9a47ef28b4fc1413e00c1d64bdf 100644
--- a/chrome/browser/sync/engine/process_commit_response_command_unittest.cc
+++ b/chrome/browser/sync/engine/process_commit_response_command_unittest.cc
@@ -53,6 +53,9 @@ class ProcessCommitResponseCommandTestWithParam
 
     commit_set_.reset(new sessions::OrderedCommitSet(routing_info()));
     SyncerCommandTestWithParam<T>::SetUp();
+    // Need to explicitly use this-> to avoid obscure template
+    // warning.
+    this->ExpectNoGroupsToChange(command_);
   }
 
  protected:
@@ -233,6 +236,7 @@ TEST_F(ProcessCommitResponseCommandTest, MultipleCommitIdProjections) {
   CreateUnprocessedCommitResult(autofill_id2, id_factory_.root(),
                                 "Autofill 2", syncable::AUTOFILL);
 
+  ExpectGroupsToChange(command_, GROUP_UI, GROUP_DB);
   command_.ExecuteImpl(session());
 
   ScopedDirLookup dir(syncdb()->manager(), syncdb()->name());
@@ -324,6 +328,7 @@ TEST_F(ProcessCommitResponseCommandTest, NewFolderCommitKeepsChildOrder) {
   // 25 items.  This should apply the values indicated by
   // each CommitResponse_EntryResponse to the syncable Entries.  All new
   // items in the commit batch should have their IDs changed to server IDs.
+  ExpectGroupToChange(command_, GROUP_UI);
   command_.ExecuteImpl(session());
 
   ScopedDirLookup dir(syncdb()->manager(), syncdb()->name());
@@ -428,6 +433,7 @@ TEST_P(MixedResult, ExtensionActivity) {
     (*records)["xyz"].extension_id = "xyz";
     (*records)["xyz"].bookmark_write_count = 4U;
   }
+  ExpectGroupsToChange(command_, GROUP_UI, GROUP_DB);
   command_.ExecuteImpl(session());
 
   ExtensionsActivityMonitor::Records final_monitor_records;