Added bluetooth LE support on Mac platform

device/bluetooth/bluetooth_discovery_manager_mac.h

Index: device/bluetooth/bluetooth_discovery_manager_mac.h
diff --git a/device/bluetooth/bluetooth_discovery_manager_mac.h b/device/bluetooth/bluetooth_discovery_manager_mac.h
index 534646aec36b31b3aeb9eb6e77803642be78ce75..f6a003c7bd35279b65ac39bc721e7731a3ce6b80 100644
--- a/device/bluetooth/bluetooth_discovery_manager_mac.h
+++ b/device/bluetooth/bluetooth_discovery_manager_mac.h
@@ -28,6 +28,9 @@ class BluetoothDiscoveryManagerMac {
     // such as when a user disables the controller, in which case the value of
     // |unexpected| will be true.
     virtual void DiscoveryStopped(bool unexpected) = 0;
+
+   protected:
+    virtual ~Observer() {}
   };
 
   virtual ~BluetoothDiscoveryManagerMac();