Fix cc preferred frame interval

cc currently will set kTwiceOfDefaultInterval when there are no
animations. This includes when user is touch scrolling.

This is ignored by FrameRateDecider in viz most of the time because
kLayerTree is not counted as fixed interval. However it matters as soon
as there is a fixed interval viz client like video. On 120hz devices,
this causes the frame rate to drop even a video is visible, even when
user is scrolling the page.

Fix by checking that there is an animation before taking using animation
interval for anything.

Bug: 1203755, 1198866
Change-Id: I4c6c1fd0424618927530a9d829e3c89abbfa6f0f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2877958


Reviewed-by: Robert Flack <flackr@chromium.org>
Reviewed-by: Zhenyao Mo <zmo@chromium.org>
Commit-Queue: Bo <boliu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#880988}