This way we don't have to rely on the existence of DEPS, and the tests
can be run in swarming bots (which don't have a checkout and therefore
don't have a DEPS file).
This seems to be where Chromium is assumming the project root path to
be.
NOTRY=True
BUG=chromium:497757
Review-Url: https://codereview.webrtc.org/2340773002
Cr-Commit-Position: refs/heads/master@{#14230}