Web Animations API: Implement DocumentTimeline.play() bindings

Change depends on https://codereview.chromium.org/150063002 (Animation Constructor bindings).

BUG=334937

Review URL: https://codereview.chromium.org/155463002

git-svn-id: svn://svn.chromium.org/blink/trunk@166954 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Evaluating media queries in link imports should use the loadingFrame's document.

Otherwise, styleForDocument grabs the null view() off the Document and bad things
ensue in Document::styleForDependentState.

BUG=341340

Review URL: https://codereview.chromium.org/139803006

git-svn-id: svn://svn.chromium.org/blink/trunk@166955 bbb929c8-8fbe-4397-9dbb-9b2b20218538