As part of this CL: https://chromium-review.googlesource.com/c/chromium/src/+/1021839 I found that this test breaks when testing the temperatures on compositors after switching to mirror mode.

WindowTreeHostManager::GetRootWindowForDisplayId(display_id) returns nullptr root window for the secondary display. It seems that the host hasn't be created, although the display ID exists in DisplayManager::GetCurrentDisplayIdList().

For now I will disable this test in mash.ash_unittests.filter.