Web Animations CSS: Hook up CSS animation play state

The modification to Player's pause logic is a temporary work-around to allow us
to pause a Player for testing, without it impacting the CSS pause logic.

Note that when the Web Animations model is exposed to JavaScript, this will
include Players and Animations generated by CSS animations. We will then have
to support such animations being manipulated from both JavaScript and CSS, and
the solution for this will avoid the need for this work-around.

BUG=258896
R=dstockwell

Review URL: https://codereview.chromium.org/27579005

git-svn-id: svn://svn.chromium.org/blink/trunk@160336 bbb929c8-8fbe-4397-9dbb-9b2b20218538
DevTools: add a warning mark to Layout events that have nested autosize

... also, generalize warnings support in Timeline.

BUG=

Review URL: https://codereview.chromium.org/29043002

git-svn-id: svn://svn.chromium.org/blink/trunk@160337 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Improve EventTarget::dispatchEvent exception error messages.

BUG=270033

Review URL: https://codereview.chromium.org/37043002

git-svn-id: svn://svn.chromium.org/blink/trunk@160338 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Auto-rebaseline for r160257

http://src.chromium.org/viewvc/blink?view=revision&revision=160257

BUG=133097
TBR=ccameron@chromium.org

Review URL: https://codereview.chromium.org/37353002

git-svn-id: svn://svn.chromium.org/blink/trunk@160339 bbb929c8-8fbe-4397-9dbb-9b2b20218538