CL 2531133002 had some problems getting past the win_chromium_rel_ng commit queue trybot, in single process mode. For example:

http://build.chromium.org/p/tryserver.chromium.win/builders/win_chromium_rel_ng/builds/343512

links to

https://luci-logdog.appspot.com/v/?s=chromium%2Fbb%2Ftryserver.chromium.win%2Fwin_chromium_rel_ng%2F343512%2F%2B%2Frecipes%2Fsteps%2Fbrowser_tests__with_patch_%2F0%2Fstdout

which ends with

[2456:4912:1203/181810.699:FATAL:interface_endpoint_client.cc(167)] Check failed: thread_checker_.CalledOnValidThread(). 

The CL is Mojo-related, but the code itself looked good to the code reviewer (rockot). In

https://groups.google.com/a/chromium.org/forum/#!msg/chromium-mojo/BKjxN1DLdrc/vBCU5Pw5AAAJ

on the chromium-mojo mailing list, rockot furthermore said:

"Meanwhile, ChromeContentRendererClient isn't destroyed until shutdown, on the main thread. Just so happens that nothing else it owns is doing thread checks now. This seems like a bug and we should be able to tear down the ContentRendererClient before tearing down the RenderThread."

This is a filing of that bug.

https://codereview.chromium.org/2531133002/diff/80002/chrome/renderer/chrome_render_thread_observer.cc#newcode314

is the (temporary) workaround for the thread-checker introduced in that CL.