Add support for Build...ParentRevision tasks.

Bug: skia:7344
Change-Id: I458afe4abe5edff8b8ccbd5abdaf4ebbf892ee00
Reviewed-on: https://skia-review.googlesource.com/90245
Reviewed-by: Eric Boren <borenet@google.com>
Commit-Queue: Ben Wagner <benjaminwagner@google.com>
9 files changed