We have tools/release/mergeinfo.py

R=verwaest@chromium.org

Change-Id: I9afb104f5c67be5f29ef33824c1ae5a4584ea1ad
Reviewed-on: https://chromium-review.googlesource.com/836610Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Commit-Queue: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50230}