Destroy DeviceImpl when the underlying UsbDevice is disconnected.

device/usb/mojo/device_impl_unittest.cc

Index: device/usb/mojo/device_impl_unittest.cc
diff --git a/device/usb/mojo/device_impl_unittest.cc b/device/usb/mojo/device_impl_unittest.cc
index df23b01f5d49f902a69d15ca823ac5a61f1b4a28..25cc048ed68de423acd018d8f1ba23b21a2090fa 100644
--- a/device/usb/mojo/device_impl_unittest.cc
+++ b/device/usb/mojo/device_impl_unittest.cc
@@ -447,6 +447,15 @@ class USBDeviceImplTest : public testing::Test {
 
 }  // namespace
 
+TEST_F(USBDeviceImplTest, Disconnect) {
+  DevicePtr device = GetMockDeviceProxy();
+
+  base::RunLoop loop;
+  device.set_connection_error_handler(loop.QuitClosure());
+  mock_device().NotifyDeviceRemoved();
+  loop.Run();
+}
+
 TEST_F(USBDeviceImplTest, Open) {
   DevicePtr device = GetMockDeviceProxy();