The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/6d3db3b6921bfa5d3e69be71c326841d55188d3c

commit 6d3db3b6921bfa5d3e69be71c326841d55188d3c
Author: bsheedy <bsheedy@chromium.org>
Date: Tue Dec 11 20:10:31 2018

Support post-failure screenshots on Vega

Adds support for the automated post-failure screenshots in
instrumentation tests on Vega standalone headsets. The regular way of
taking screenshots (equivalent to the power button + volume down
approach) doesn't work on Vega, as it just captures a black screen
with the VR overlay.

Instead, use VrCore's RecorderService to take a screenshot on Vega.

Bug:  913077 
Change-Id: I0ddde9c32ba942f925d666aa5c30c598ce97c0a3
Reviewed-on: https://chromium-review.googlesource.com/c/1368694
Reviewed-by: John Budorick <jbudorick@chromium.org>
Commit-Queue: Brian Sheedy <bsheedy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#615637}
[modify] https://crrev.com/6d3db3b6921bfa5d3e69be71c326841d55188d3c/base/test/android/javatests/src/org/chromium/base/test/ScreenshotOnFailureStatement.java
[modify] https://crrev.com/6d3db3b6921bfa5d3e69be71c326841d55188d3c/build/android/pylib/local/device/local_device_instrumentation_test_run.py
[modify] https://crrev.com/6d3db3b6921bfa5d3e69be71c326841d55188d3c/chrome/android/shared_preference_files/test/vr_ddview_skipdon_setupcomplete.json

This is in and functional, but not useful if the failed test doesn't use the mocked head/controller input since the device won't be pointed at the virtual screen.

We could fix this by using reflection to try to enable mocked input before taking the screenshot, but doing actual work like that outside of a test doesn't seem like a good idea.