Implement AssistantProgressIndicator motion spec.

Still missing tweens. Need to discuss with UX about potentially revising
specs to use pre-defined tweens.

See bug for demo.

Bug: b:111573788
Change-Id: I7d94416afa834d83aafa7e1e5f8eb9d6efe44333
Reviewed-on: https://chromium-review.googlesource.com/1144197
Commit-Queue: David Black <dmblack@google.com>
Reviewed-by: Xiaohui Chen <xiaohuic@chromium.org>
Cr-Commit-Position: refs/heads/master@{#577765}
5 files changed