Implement BluetoothRemoteGattCharacteristicWin::StartNotifySession and related unit tests

device/bluetooth/bluetooth_low_energy_win.h

Index: device/bluetooth/bluetooth_low_energy_win.h
diff --git a/device/bluetooth/bluetooth_low_energy_win.h b/device/bluetooth/bluetooth_low_energy_win.h
index cd7150d18418ec73e53fd89f17cc346eb4ba7028..f3636f4fe6f7376438b7e0ea7b8e7a1a6a0d5671 100644
--- a/device/bluetooth/bluetooth_low_energy_win.h
+++ b/device/bluetooth/bluetooth_low_energy_win.h
@@ -176,6 +176,19 @@ class DEVICE_BLUETOOTH_EXPORT BluetoothLowEnergyWrapper {
       const PBTH_LE_GATT_CHARACTERISTIC characteristic,
       PBTH_LE_GATT_CHARACTERISTIC_VALUE new_value);
 
+  // Register GATT events of |event_type| in the service with service device
+  // path |service_path|. |event_parameter| is the event's parameter. |callback|
+  // is the function to be invoked if the event happened. |context| is the input
+  // parameter to be given back through |callback|. |*out_handle| stores the
+  // unique handle in OS for this registration.

[ortuno, 2016/03/15 02:55:31]

Could you add here that this function will write to the CCC descriptor?

[gogerald1, 2016/03/15 18:28:22]

May not good since I do not see Windows implementation code. OS may implement it
in another way, like polling.

[gogerald1, 2016/03/17 14:07:56]

Add similar comments in bluetooth_remote_gatt_characteristic_win.cc

[ortuno, 2016/03/21 17:00:52]

I thought you said you tested it and it does write to the descriptor?

[gogerald1, 2016/03/21 22:09:16]

No, I said I tested the functionality of these interfaces, for this interface it
means I can receive characteristic value change notification from my mobile
after calling this interface.

[ortuno, 2016/03/22 15:02:24]

Maybe a little context will make it clear why we need to know if the descriptor
was written. Devices that support notifications are not always sending out
notifications. They only start sending notifications once the CCC descriptor has
been written to. If Windows doesn't write to the descriptor then we are going to
start getting reports of people not getting any notifications from their
devices. So please find out whether or not BluetoothGATTRegisterEvent writes to
the CCC descriptor or not.

[gogerald1, 2016/03/29 15:12:00]

Done. From HCI log, Windows does not write CCCD implicitly, modified by setting
CCCD explicitly, verified by HCI log.

+  virtual HRESULT RegisterGattEvents(base::FilePath& service_path,
+                                     BTH_LE_GATT_EVENT_TYPE event_type,
+                                     PVOID event_parameter,
+                                     PFNBLUETOOTH_GATT_EVENT_CALLBACK callback,
+                                     PVOID context,
+                                     BLUETOOTH_GATT_EVENT_HANDLE* out_handle);
+  virtual HRESULT UnregisterGattEvent(BLUETOOTH_GATT_EVENT_HANDLE event_handle);
+
  protected:
   BluetoothLowEnergyWrapper();
   virtual ~BluetoothLowEnergyWrapper();