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

chrome/browser/sync/engine/verify_updates_command.cc

Index: chrome/browser/sync/engine/verify_updates_command.cc
diff --git a/chrome/browser/sync/engine/verify_updates_command.cc b/chrome/browser/sync/engine/verify_updates_command.cc
index 81f1de286a9c7a5babae4a7f03ff2a322808a359..04b44f914bae40554d8fbb6d9c4d539df2da932b 100644
--- a/chrome/browser/sync/engine/verify_updates_command.cc
+++ b/chrome/browser/sync/engine/verify_updates_command.cc
@@ -27,6 +27,26 @@ using syncable::SYNCER;
 VerifyUpdatesCommand::VerifyUpdatesCommand() {}
 VerifyUpdatesCommand::~VerifyUpdatesCommand() {}
 
+bool VerifyUpdatesCommand::HasCustomGroupsToChange() const {
+  // TODO(akalin): Set to true.
+  return false;
+}
+
+std::set<ModelSafeGroup> VerifyUpdatesCommand::GetGroupsToChange(
+    const sessions::SyncSession& session) const {
+  std::set<ModelSafeGroup> groups_with_updates;
+
+  const GetUpdatesResponse& updates =
+      session.status_controller().updates_response().get_updates();
+  for (int i = 0; i < updates.entries().size(); i++) {
+    groups_with_updates.insert(
+        GetGroupForModelType(syncable::GetModelType(updates.entries(i)),
+                             session.routing_info()));
+  }
+
+  return groups_with_updates;
+}
+
 void VerifyUpdatesCommand::ModelChangingExecuteImpl(
     sessions::SyncSession* session) {
   DVLOG(1) << "Beginning Update Verification";