device/bluetooth: Add abstract API definition for BluetoothGattDescriptor.

device/bluetooth/bluetooth_gatt_service.h

 // 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.
 
 #ifndef DEVICE_BLUETOOTH_GATT_SERVICE_H_
 #define DEVICE_BLUETOOTH_GATT_SERVICE_H_
 
 #include <vector>
 
 #include "base/basictypes.h"
@@ skipping 129 matching lines @@
         BluetoothGattService* service,
         const std::vector<BluetoothGattService*>& included_services) {}
 
     // Called when the characteristics that belong to |service| have changed.
     virtual void CharacteristicsChanged(
         BluetoothGattService* service,
         const std::vector<BluetoothGattCharacteristic*>& characteristics) {}
   };
 
   // The ErrorCallback is used by methods to asynchronously report errors.
-  typedef base::Callback<const std::string&> ErrorCallback;
+  typedef base::Callback<void(const std::string&)> ErrorCallback;
 
   // Constructs a BluetoothGattService that can be locally hosted when the local
   // adapter is in the peripheral role. The resulting object can then be made
   // available by calling the "Register" method. This method constructs a
   // service with UUID |uuid|. Whether the constructed service is primary or
   // secondary is determined by |is_primary|. |delegate| is used to send certain
   // peripheral role events. If |delegate| is NULL, then this service will
   // employ a default behavior when responding to read and write requests based
   // on the cached value of its characteristics and descriptors at a given time.
   static BluetoothGattService* Create(const bluetooth_utils::UUID& uuid,
@@ skipping 56 matching lines @@
   BluetoothGattService();
   virtual ~BluetoothGattService();
 
  private:
   DISALLOW_COPY_AND_ASSIGN(BluetoothGattService);
 };
 
 }  // namespace device
 
 #endif  // DEVICE_BLUETOOTH_GATT_SERVICE_H_