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

device/bluetooth/bluetooth_adapter.cc

Index: device/bluetooth/bluetooth_adapter.cc
diff --git a/device/bluetooth/bluetooth_adapter.cc b/device/bluetooth/bluetooth_adapter.cc
index 7b30fad19ebd8a1f5ce5d300142767bf306fe234..d39a73adcef27eece593125009f3c215b84e75b5 100644
--- a/device/bluetooth/bluetooth_adapter.cc
+++ b/device/bluetooth/bluetooth_adapter.cc
@@ -55,6 +55,10 @@ void BluetoothAdapter::RemoveObserver(BluetoothAdapter::Observer* observer) {
   observers_.RemoveObserver(observer);
 }
 
+bool BluetoothAdapter::HasObserver(BluetoothAdapter::Observer* observer) {
+  return observers_.HasObserver(observer);

[rkc, 2016/08/08 23:53:33]

Before this line,
DCHECK(observer);

[puthik_chromium, 2016/08/09 00:08:57]

Added.
Actually, It would just return false if observer is null anyway.

+}
+
 void BluetoothAdapter::StartDiscoverySession(
     const DiscoverySessionCallback& callback,
     const ErrorCallback& error_callback) {