Migrate time_to_next_iteration to AnimationTimeDelta

It's currently using a double to represent a duration. Migrated to
AnimationTimeDelta to ease the migration from doubles to base::Time*
types.

Bug: 737867
Change-Id: I53ca0cad341ea7c6b5068edef070b202d7174733
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1982543
Reviewed-by: Kevin Ellis <kevers@chromium.org>
Commit-Queue: Sergio Villar <svillar@igalia.com>
Cr-Commit-Position: refs/heads/master@{#728181}
9 files changed