Bug 1041440: Create Promise using |Promise::Create|, r=btian

This patch fixes a call to the private constructor of |Promise|.

dom/bluetooth2/BluetoothAdapter.cpp

@@ -457,7 +457,10 @@ BluetoothAdapter::StopDiscovery(ErrorResult& aRv)
     aRv.Throw(NS_ERROR_FAILURE);
     return nullptr;
   }
-  nsRefPtr<Promise> promise = new Promise(global);
+  nsRefPtr<Promise> promise = Promise::Create(global, aRv);
+  if (aRv.Failed()) {
+    return nullptr;
+  }
 
   /**
    * Ensure