Can reproduce with: ./out/cros/interactive_ui_tests --enable-features=Mash --gtest_filter=DownloadNotificationTest.IncognitoDownloadFile

In this test I see two ClientRoots being created. One is the top_level, while the other is not.

The non-top_level ClientRoot is set to not assign LocalSurfaceIds (it's ServerWindow has an owning tree. However the client never sends the Window Service a valid LocalSurfaceId. So it fails to embed.

The connection itself seems to only be partially complete.
  -  ClientRoot::HandleBoundsOrScaleFactorChange attempts to notify the WindowTreeClient, but that message is just being enqueued. No WindowTreeClient seems to receive it
  -  WindowTree::SetWindowBounds is being called by the client, though with an invalid LocalSurfaceId.

So it appears that the client is around, but that the connections are being fully setup. Any ideas?