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

chrome/browser/sync/engine/process_updates_command.cc

Index: chrome/browser/sync/engine/process_updates_command.cc
diff --git a/chrome/browser/sync/engine/process_updates_command.cc b/chrome/browser/sync/engine/process_updates_command.cc
index 367be000a8463ffc7d09b3d6915300a64881ef2e..5a2f4fece746267163560124c7accaddaa93af2f 100644
--- a/chrome/browser/sync/engine/process_updates_command.cc
+++ b/chrome/browser/sync/engine/process_updates_command.cc
@@ -22,10 +22,32 @@ namespace browser_sync {
 
 using sessions::SyncSession;
 using sessions::StatusController;
+using sessions::UpdateProgress;
 
 ProcessUpdatesCommand::ProcessUpdatesCommand() {}
 ProcessUpdatesCommand::~ProcessUpdatesCommand() {}
 
+std::set<ModelSafeGroup> ProcessUpdatesCommand::GetGroupsToChange(
+    const sessions::SyncSession& session) const {
+  std::set<ModelSafeGroup> groups_with_verified_updates;
+
+  const std::set<ModelSafeGroup>& active_groups =
+      ModelChangingSyncerCommand::GetActiveGroups(session);
+
+  for (std::set<ModelSafeGroup>::const_iterator it =
+           active_groups.begin(); it != active_groups.end(); ++it) {
+    const UpdateProgress* update_progress =
+        session.status_controller().GetUnrestrictedUpdateProgress(*it);
+    if (update_progress &&
+        (update_progress->VerifiedUpdatesBegin() !=
+         update_progress->VerifiedUpdatesEnd())) {
+      groups_with_verified_updates.insert(*it);
+    }
+  }
+
+  return groups_with_verified_updates;
+}
+
 bool ProcessUpdatesCommand::ModelNeutralExecuteImpl(SyncSession* session) {
   const GetUpdatesResponse& updates =
       session->status_controller().updates_response().get_updates();