arc: bluetooth: Add/Remove BT observer only when ARC is ready

device/bluetooth/bluetooth_adapter.h

Index: device/bluetooth/bluetooth_adapter.h
diff --git a/device/bluetooth/bluetooth_adapter.h b/device/bluetooth/bluetooth_adapter.h
index 5e2e82607c76e97413c5e63bc38426990a807f9d..c8daff2629d5a4e064388bb6c0a28c59bb8aab2e 100644
--- a/device/bluetooth/bluetooth_adapter.h
+++ b/device/bluetooth/bluetooth_adapter.h
@@ -267,6 +267,7 @@ class DEVICE_BLUETOOTH_EXPORT BluetoothAdapter
   // methods to determine which adapter is issuing the event.
   virtual void AddObserver(BluetoothAdapter::Observer* observer);
   virtual void RemoveObserver(BluetoothAdapter::Observer* observer);
+  virtual bool HasObserver(BluetoothAdapter::Observer* observer);
 
   // The address of this adapter. The address format is "XX:XX:XX:XX:XX:XX",
   // where each XX is a hexadecimal number.