Revert of Web Animations: Use a single animation clock

Revert of Web Animations: Use a single animation clock (patchset #7 id:120001 of https://codereview.chromium.org/1410313004/ )

Reason for revert:
Still breaks the Android bot (at least): https://build.chromium.org/p/chromium.webkit/waterfall?show=WebKit%20Android%20(Nexus4)

Please do not reland without first ensuring you have run the webkit_unit_tests step a few times on an equivalent Android bot.

Original issue's description:
> Web Animations: Use a single animation clock
>
> All animation clocks for a page should tick at the same time, but since we
> had an animation clock per document there were some cases where clocks
> could tick independently.
>
> This patch moves the clock from Document to PageAnimator.
> animation-timeline-detached-no-crash.html is removed as the test was not valid
> due to the animation's document not being active.
>
> Committed: https://crrev.com/b45c39903df3727d21cbc217a0b14c2c85b0715a
> Cr-Commit-Position: refs/heads/master@{#356776}
>
> Committed: https://crrev.com/ddd06a6080e1e7d7d02b15595289940980b04973
> Cr-Commit-Position: refs/heads/master@{#357044}

TBR=samli@chromium.org,dstockwell@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true

Committed: https://crrev.com/7e4c010fc4a6ec7672f19ca901e9da1175f0abf0
Cr-Commit-Position: refs/heads/master@{#357050}

[Peter Kasting, 2015-10-30 07:45:50]

Created Revert of Web Animations: Use a single animation clock

[commit-bot: I haz the power, 2015-10-30 07:46:19]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1425143006/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1425143006/1

[commit-bot: I haz the power, 2015-10-30 07:47:17]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-10-30 07:48:19]

Patchset 1 (id:??) landed as
https://crrev.com/7e4c010fc4a6ec7672f19ca901e9da1175f0abf0
Cr-Commit-Position: refs/heads/master@{#357050}