tree 1ae61ebc5ba1b5738ae47762c2c5f471dced3386
parent 5a674b79a074c582550cdf99756f23619d9c09b8
author Stephen Li <stephenli@google.com> 1491005999 -0700
committer Stephen Li <stephenli@google.com> 1491381646 -0700

Use RevWalk from CommitReceivedEvent

When cherry-picking changes through the UI, we can be referencing
a tree SHA that hasn't been flushed yet. Use the RevWalk handed
down by CommitReceivedEvent so that we can parse this tree SHA.

Change-Id: Id64599f6d29732996efeaf3c7c1c15b70d61fc39