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

chrome/browser/sync/engine/process_commit_response_command.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 "chrome/browser/sync/engine/process_commit_response_command.h"
 
+#include <cstddef>
 #include <set>
 #include <string>
 #include <vector>
 
 #include "base/basictypes.h"
 #include "base/location.h"
 #include "chrome/browser/sync/engine/syncer_proto_util.h"
 #include "chrome/browser/sync/engine/syncer_util.h"
 #include "chrome/browser/sync/engine/syncproto.h"
 #include "chrome/browser/sync/sessions/sync_session.h"
@@ skipping 35 matching lines @@
 void IncrementErrorCounters(StatusController* status) {
   status->increment_num_consecutive_errors();
 }
 void ResetErrorCounters(StatusController* status) {
   status->set_num_consecutive_errors(0);
 }
 
 ProcessCommitResponseCommand::ProcessCommitResponseCommand() {}
 ProcessCommitResponseCommand::~ProcessCommitResponseCommand() {}
 
+std::set<ModelSafeGroup> ProcessCommitResponseCommand::GetGroupsToChange(
+    const sessions::SyncSession& session) const {
+  std::set<ModelSafeGroup> groups_with_commits;
+  syncable::ScopedDirLookup dir(session.context()->directory_manager(),
+                                session.context()->account_name());
+  if (!dir.good()) {
+    LOG(ERROR) << "Scoped dir lookup failed!";
+    return groups_with_commits;
+  }
+
+  syncable::ReadTransaction trans(FROM_HERE, dir);
+  const StatusController& status = session.status_controller();
+  for (size_t i = 0; i < status.commit_ids().size(); ++i) {
+    groups_with_commits.insert(
+        GetGroupForModelType(status.GetUnrestrictedCommitModelTypeAt(i),
+                             session.routing_info()));
+  }
+
+  return groups_with_commits;
+}
+
 bool ProcessCommitResponseCommand::ModelNeutralExecuteImpl(
     sessions::SyncSession* session) {
   ScopedDirLookup dir(session->context()->directory_manager(),
                       session->context()->account_name());
   if (!dir.good()) {
     LOG(ERROR) << "Scoped dir lookup failed!";
     return false;
   }
 
   const StatusController& status = session->status_controller();
@@ skipping 413 matching lines @@
   // been recursively deleted.
   // TODO(nick): Here, commit_message.deleted() would be more correct than
   // local_entry->Get(IS_DEL).  For example, an item could be renamed, and then
   // deleted during the commit of the rename.  Unit test & fix.
   if (local_entry->Get(IS_DIR) && local_entry->Get(IS_DEL)) {
     deleted_folders->insert(local_entry->Get(ID));
   }
 }
 
 }  // namespace browser_sync