[SyncFS] Introduce CallbackTracker to handle callback abortion

chrome/browser/sync_file_system/drive_backend/callback_tracker.cc

+// Copyright 2014 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_file_system/drive_backend/callback_tracker.h"
+
+#include <algorithm>
+
+namespace sync_file_system {
+namespace drive_backend {
+
+CallbackTracker::CallbackTracker() {
+}
+
+CallbackTracker::~CallbackTracker() {
+  AbortAll();
+}
+
+void CallbackTracker::AbortAll() {
+  AbortClosureByHelper helpers;
+  std::swap(helpers, helpers_);
+  for (AbortClosureByHelper::iterator itr = helpers.begin();
+       itr != helpers.end(); ++itr) {
+    delete itr->first;
+    itr->second.Run();
+  }
+}
+
+scoped_ptr<internal::AbortHelper> CallbackTracker::PassAbortHelper(
+    internal::AbortHelper* helper) {
+  if (helpers_.erase(helper) == 1)
+    return scoped_ptr<internal::AbortHelper>(helper);
+  return scoped_ptr<internal::AbortHelper>();
+}
+
+}  // namespace drive_backend
+}  // namespace sync_file_system