Add a mocked FakeAppUpdateManager for simulating inline updates

Add the ability to simulate an inline update flow, which will be used by variations,
test, and PM/UX to look at the update flow.

BUG=922714

Change-Id: Ic313e8cae6e9fc9f0413c227c151990d192e62a5
Reviewed-on: https://chromium-review.googlesource.com/c/1461831
Reviewed-by: Tommy Nyquist <nyquist@chromium.org>
Reviewed-by: David Trainor <dtrainor@chromium.org>
Cr-Commit-Position: refs/heads/master@{#632018}
4 files changed