Implement BluetoothLowEnergyWrapperFake for Bluetooth test fixture

device/bluetooth/test/bluetooth_test.h

Index: device/bluetooth/test/bluetooth_test.h
diff --git a/device/bluetooth/test/bluetooth_test.h b/device/bluetooth/test/bluetooth_test.h
index 7191345d10e22557081c59895a2a3fbadaa6bdcb..5e34d909d8666a6f1408a95cc4cb8ca38fc2de69 100644
--- a/device/bluetooth/test/bluetooth_test.h
+++ b/device/bluetooth/test/bluetooth_test.h
@@ -58,7 +58,7 @@ class BluetoothTestBase : public testing::Test {
   // Calls adapter_->StartDiscoverySessionWithFilter with Low Energy transport,
   // and this fixture's callbacks expecting success.
   // Then RunLoop().RunUntilIdle().
-  void StartLowEnergyDiscoverySession();
+  virtual void StartLowEnergyDiscoverySession();
 
   // Calls adapter_->StartDiscoverySessionWithFilter with Low Energy transport,
   // and this fixture's callbacks expecting error.