Remove the MessageLoop::DestructionObserver from mojo bindings.

device/bluetooth/device_unittest.cc

Index: device/bluetooth/device_unittest.cc
diff --git a/device/bluetooth/device_unittest.cc b/device/bluetooth/device_unittest.cc
index 51e150efed5a3588f0a5d94bf638b74477d2f76f..c2ca53f6926846105eff781dd26d5672e62661e9 100644
--- a/device/bluetooth/device_unittest.cc
+++ b/device/bluetooth/device_unittest.cc
@@ -141,6 +141,7 @@ class BluetoothInterfaceDeviceTest : public testing::Test {
     EXPECT_EQ(expected_success_callback_calls_, actual_success_callback_calls_);
     EXPECT_EQ(message_pipe_closed_, expect_device_service_deleted_);
     proxy_.reset();
+    base::RunLoop().RunUntilIdle();
   }
 
  protected: