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
21 files changed
tree: 1ae61ebc5ba1b5738ae47762c2c5f471dced3386
  1. .settings/
  2. src/
  3. .gitignore
  4. BUILD
  5. external_plugin_deps.bzl
  6. LICENSE