Includes necessary DEPS and GN build changes.
Some folders are copied directly from Chromium because they don't
exist as source mirrors or aren't available for other reasons.

Bug: angleproject:2344
Change-Id: Ibb7f8a3e2288048b7aed2b0e277ca63b5a932c57
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2826480
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Yuly Novikov <ynovikov@chromium.org>