Chrome Version: 60.0.3102.0

The new EditingTest.RichTextMoveByLine test, added in this CL
  https://codereview.chromium.org/2540553002
is flaking on the Linux ChromiumOS Tests builder.  It seems to fail (time out) roughly half the time, but usually passes on a subsequent retry.

Here's an example where the builder (all retries) failed:
https://build.chromium.org/p/chromium.chromiumos/builders/Linux%20ChromiumOS%20Tests%20%281%29/builds/38768

I've saved the relevant part of stdout from chromevox_tests to https://paste.googleplex.com/4905578551836672.

I was able to reproduce a timeout locally after several tries (debug build).