Add more helpers for interfacing with Gerrit.
Move dawn-specific constants out to a new 'dawn' package. Keeps the
packages dawn-specific-free.
Bug: dawn:1342
Change-Id: Iaebe0b68d877340fc848d711c848d01705ddae57
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/86524
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Ben Clayton <bclayton@chromium.org>
Kokoro: Kokoro <noreply+kokoro@google.com>
Ben Clayton