Web Animations: Update outdated players as part of the render tree update

In Web Animations, updates to the animation model are live[1] and should be
visible immediately to queries. In Blink, updating of the model is deferred
until necessary. Previously there were hooks in getComputedStyle and following
animation frame callbacks[2]. However these were not sufficient to cover all
forms of effect queries, eg. synchronous layouts. This patch ensures that
animation timing is always brought up to date as part of the render tree
update. This has the additional benefit that the timing update following
animation frame callbacks can be deferred.

[1] http://dev.w3.org/fxtf/web-animations/#script-execution-and-live-updates-to-the-model
[2] https://src.chromium.org/viewvc/blink?view=rev&revision=170169

Review URL: https://codereview.chromium.org/256063004

git-svn-id: svn://svn.chromium.org/blink/trunk@172844 bbb929c8-8fbe-4397-9dbb-9b2b20218538