Add a SharedMemSynchronizer class.

media/audio/cross_process_notification.cc

+// Copyright (c) 2012 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 "media/audio/cross_process_notification.h"
+
+#include "base/logging.h"
+#include "base/memory/scoped_ptr.h"
+
+CrossProcessNotification::CrossProcessNotification() {}
+
+CrossProcessNotification::WaitForMultiple::WaitForMultiple(
+    const Notifications* notifications) {
+  Reset(notifications);
+}
+
+int CrossProcessNotification::WaitForMultiple::Wait() {
+  DCHECK(CalledOnValidThread());
+  int ret = WaitMultiple(*notifications_, wait_offset_);
+  wait_offset_ = (ret + 1) % notifications_->size();
+  return ret;
+}
+
+void CrossProcessNotification::WaitForMultiple::Reset(
+    const Notifications* notifications) {
+  DCHECK(CalledOnValidThread());
+  wait_offset_ = 0;
+  notifications_ = notifications;
+  DCHECK(!notifications_->empty());
+}