Add implementation for parsing device info in read/write attribute calls.

device/bluetooth/dbus/bluetooth_gatt_attribute_helpers.h

+// Copyright 2016 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 DEVICE_BLUETOOTH_DBUS_BLUETOOTH_GATT_ATTRIBUTES_HELPER_H_
+#define DEVICE_BLUETOOTH_DBUS_BLUETOOTH_GATT_ATTRIBUTES_HELPER_H_
+
+#include "dbus/object_path.h"
+
+namespace dbus {
+class MessageReader;
+}
+
+namespace bluez {
+
+// Helper methods used from various GATT attribute providers and clients.
+dbus::ObjectPath ReadDevicePath(dbus::MessageReader* reader);
+
+}  // namespace bluez
+
+#endif  // DEVICE_BLUETOOTH_DBUS_BLUETOOTH_GATT_ATTRIBUTES_HELPER_H_