Implement BluetoothRemoteGattCharacteristicWin::GetDescriptors

device/bluetooth/bluetooth_low_energy_win.cc

Index: device/bluetooth/bluetooth_low_energy_win.cc
diff --git a/device/bluetooth/bluetooth_low_energy_win.cc b/device/bluetooth/bluetooth_low_energy_win.cc
index 1e985b54f1b00b2b771c61374519a5c76a19490b..3e2c7c2a900a0c387bcb73b261545dc5d2ba8037 100644
--- a/device/bluetooth/bluetooth_low_energy_win.cc
+++ b/device/bluetooth/bluetooth_low_energy_win.cc
@@ -757,5 +757,42 @@ HRESULT BluetoothLowEnergyWrapper::ReadCharacteristicsOfAService(
   return hr;
 }
 
+HRESULT BluetoothLowEnergyWrapper::ReadDescriptorsOfACharacteristic(
+    base::FilePath& service_path,
+    const PBTH_LE_GATT_CHARACTERISTIC characteristic,
+    scoped_ptr<BTH_LE_GATT_DESCRIPTOR>* out_included_descriptors,
+    USHORT* out_counts) {
+  base::File file(service_path, base::File::FLAG_OPEN | base::File::FLAG_READ);
+  if (!file.IsValid())
+    return HRESULT_FROM_WIN32(ERROR_OPEN_FAILED);
+
+  USHORT required_length = 0;
+  HRESULT hr = BluetoothGATTGetDescriptors(
+      file.GetPlatformFile(), characteristic, 0, NULL, &required_length,
+      BLUETOOTH_GATT_FLAG_NONE);
+  if (hr != HRESULT_FROM_WIN32(ERROR_MORE_DATA))
+    return hr;
+
+  out_included_descriptors->reset(new BTH_LE_GATT_DESCRIPTOR[required_length]);
+  USHORT actual_length = required_length;

[scheib, 2016/03/01 00:06:22]

I overlooked that you did not address this in previous patch: 
https://codereview.chromium.org/1690133002/diff/80001/device/bluetooth/blueto...
Please respond to all review comments raised.

Please address here and in ::ReadIncludedServicesOfAService to improve
readability.

[gogerald1, 2016/03/01 17:00:13]

Done.

+  hr = BluetoothGATTGetDescriptors(file.GetPlatformFile(), characteristic,
+                                   actual_length,
+                                   out_included_descriptors->get(),
+                                   &required_length, BLUETOOTH_GATT_FLAG_NONE);
+  if (SUCCEEDED(hr) && required_length != actual_length) {
+    LOG(ERROR) << "Retrieved # of descriptors is not equal to expected"
+               << " actual_length " << actual_length << " required_length "
+               << required_length;
+    hr = HRESULT_FROM_WIN32(ERROR_INVALID_USER_BUFFER);
+  }
+  *out_counts = actual_length;
+
+  if (FAILED(hr)) {
+    out_included_descriptors->reset(nullptr);
+    *out_counts = 0;
+  }
+  return hr;
+}
+
 }  // namespace win
 }  // namespace device