As of https://build.chromium.org/p/chromium.fyi/builders/Mojo%20ChromiumOS/builds/20873

mash_browser_tests have begun constantly timing out.

I can reproduce this locally.

What is happening is that the destructor of BackgroundServiceManager can block waiting on a background thread.

In these cases:
BackgroundServiceManager::ShutDownOnBackgroundThread is being called, but for some reason the signal back to the main thread never gets through....

Unlike my original suspicions in  issue 754716  this isn't rockot@'s change. Simply timing changes have exposed this. Both of us running at the same revision are seeing different behaviours.

Need to debug further