commit 35c2a0c08dcbf7368d699a91603cd46b42aaef1c
author Majid Valipour <majidvp@chromium.org> Fri Feb 08 23:53:30 2019
committer Commit Bot <commit-bot@chromium.org> Fri Feb 08 23:53:30 2019
tree a3cd9dc65ad7b2dcd68d001aebb73f55bc00c228
parent 545a25e8c0d56ba1d0efa98a648a8549bae3eb28

[animation-worklet] Basic pause implementation (reland)

Pausing worklet animation now holds the time. This works as expected for main
thread animations. Implementing this for composited worklet animations will be
done in a follow up patch.

Major changes:
 - Add and expose pause() method pausing the animation.
 - Introduce hold_time that is used when animation is paused.
 - Rework how current time is computed, it is now closer to
   regular animations i.e., we either compute it based on "start time and
   timeline.currentTime" or use "hold time".
 - Instead of setting start time we now set the current time
   which then works backward to compute either the start time or the hold time
   based on the animation state.
 - When transitioning animation play state, we now always set
   the current time. Previously this was adhoc and inconsistent.
 - Introduce has_started_ to differentiate when playing an
   animation for the first time vs playing it from pause.
 - Update playback_rate related calculation to use new logic.



Relanding: Original CL was reverted here [1]. Took the following steps to
address this:

  - Address flakiness in unit test by using more accurate error
    value matching other tests.
  - Fix flakiness in layout test (worklet-animation-pause.https.html)
    by using startTime and waiting for time to actually advance working around
    pre-existing animation clock issue [2]. Also got rid of an invalid state
    transition from pause->idle.

[1] https://chromium-review.googlesource.com/c/chromium/src/+/1434815
[2] http://crbug.com/785940

TEST:

  - wpt/animation-worklet/worklet-animation-pause.https.html: js test for basic
    current time calculations
  - wpt/animation-worklet/worklet-animation-pause-immediately.https.html:
    reftest for basic pause
  - wpt/animation-worklet/worklet-animation-pause-result.https.html: reftest for
    pause/resume.
  - WorkletAnimationTest.PausePlay: unit test for basic state
    transition and time calc

Bug: 821910,
Change-Id: I11fd2960443081be81055904d6d56a2abc3282f5
Reviewed-on: https://chromium-review.googlesource.com/c/1456640
Reviewed-by: Majid Valipour <majidvp@chromium.org>
Reviewed-by: Yi Gu <yigu@chromium.org>
Commit-Queue: Majid Valipour <majidvp@chromium.org>
Cr-Commit-Position: refs/heads/master@{#630548}