GitLab

This adds external devtools frontend as DEPS, but does not
start using it except for scripts and documentation. Build
and tests are not affected.

Bug: 1011259
Change-Id: I3b6173582bf88974784f6d758ad91b6f740b1b26
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1855740
Commit-Queue: Yang Guo <yangguo@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Reviewed-by: Andrew Grieve <agrieve@chromium.org>
Reviewed-by: Marc Treib <treib@chromium.org>
Cr-Commit-Position: refs/heads/master@{#707730}