GitLab

Also adds diff_test.cc.

Bug: 1011921
Change-Id: I3d678738719531d1c74e620f4fc3605cab08b325
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1918027
Commit-Queue: Jasper Chapman-Black <jaspercb@chromium.org>
Reviewed-by: Andrew Grieve <agrieve@chromium.org>
Reviewed-by: Samuel Huang <huangs@chromium.org>
Cr-Commit-Position: refs/heads/master@{#715841}