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 6493e3d86d31b2456f7a0ce3d49e71cd5b40cdbd..f89f47467317de21713c587998d5537597ac2bfb 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: