Implement isInTestingMode (migration to CompositorAnimator, part 2)

This is part of changes which put as goal removing redundant ChromeAnimation API by moving everything into CompositorAnimator.

Public doc with proposal: https://docs.google.com/document/d/1VL5ntE7vn267IFjE4Zke0GkhVVTHz1bEP672Apj_E2k/edit

This concrete patch is implementing isInTestingMode, which will replace animationMultiplier in tests (ChromeAnimationTest using old animationMultiplier will be removed with next patches in this series).

BUG=890643

Change-Id: I42e19e165c5d91ae13e0dd719b80d000a9b712e2
Reviewed-on: https://chromium-review.googlesource.com/c/1375109
Reviewed-by: Matthew Jones <mdjones@chromium.org>
Reviewed-by: David Trainor <dtrainor@chromium.org>
Commit-Queue: Marcin Wiącek <marcin@mwiacek.com>
Cr-Commit-Position: refs/heads/master@{#629694}
7 files changed