Merge the multiple frame tree walks in PageAnimator::serviceScriptedAnimations.

Merge the multiple frame tree walks in PageAnimator::serviceScriptedAnimations.

There's no real reason to do all this work in multiple passes over the Vector
of Documents. This change does alter the web exposed behavior slightly since
now given two same origin iframes that are siblings in the frame tree:

   A
  / \
 B   C

when B runs if it looks at C's scroll position during a scroll animation and
SMIL animation state it may see slightly different results, especially if the
B frame actually started the animation in the C frame. This is already very
racing and unpredictable in browsers since it's an obscure edge case, so I'm
not too worried it'll break content.

This will allow easily skipping iframes that are still loading when processing
the blink pipeline.

BUG=521692
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=200761

[esprehn, 2015-08-18 21:05:29]

The CQ bit was checked by esprehn@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2015-08-18 21:05:39]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1298253003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1298253003/1

[esprehn, 2015-08-18 21:59:47]

esprehn@chromium.org changed reviewers:
+ dglazkov@chromium.org, ojan@chromium.org

[ojan, 2015-08-18 22:01:58]

lgtm

[esprehn, 2015-08-18 22:09:05]

esprehn@chromium.org changed reviewers:
+ skyostil@chromium.org

[esprehn, 2015-08-18 22:10:37]

The CQ bit was unchecked by esprehn@chromium.org

[esprehn, 2015-08-18 22:10:38]

The CQ bit was checked by esprehn@chromium.org

[commit-bot: I haz the power, 2015-08-18 22:10:54]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1298253003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1298253003/1

[commit-bot: I haz the power, 2015-08-18 22:42:53]

Committed patchset #1 (id:1) as
https://src.chromium.org/viewvc/blink?view=rev&revision=200761