Add an asynchronous version of the Flash DeviceID API.

ppapi/cpp/private/flash_device_id.h

+// 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.
+
+#ifndef PPAPI_CPP_PRIVATE_FLASH_DEVICE_ID_H_
+#define PPAPI_CPP_PRIVATE_FLASH_DEVICE_ID_H_
+
+#include "ppapi/cpp/completion_callback.h"
+#include "ppapi/cpp/resource.h"
+
+namespace pp {
+namespace flash {
+
+class DeviceID : public Resource {
+ public:
+  DeviceID();
+  DeviceID(const InstanceHandle& instance);
+
+  // On success, returns a string var.
+  int32_t GetDeviceID(const CompletionCallbackWithOutput<Var>& callback);
+};
+
+}  // namespace flash
+}  // namespace pp
+
+#endif  // PPAPI_CPP_PRIVATE_FLASH_DEVICE_ID_H_