GitLab

Creates SceneActivityState enum to list possible scene states and
makes the scene delegate create and update the scene state.

Bug: none
Change-Id: I45932fefcff42828a761b6d4d53fc1c034a3102e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1789524
Commit-Queue: Stepan Khapugin <stkhapugin@chromium.org>
Auto-Submit: Stepan Khapugin <stkhapugin@chromium.org>
Reviewed-by: Mark Cogan <marq@chromium.org>
Cr-Commit-Position: refs/heads/master@{#695117}