Refactoring: Reduces the Document dependency on StyleSheet collection subclasses.

This is a cleanup that gets rid of some Document dependency.
In future change, the StyleEngine, not the Document, will lookup the appropriate
StyleResolver instance.

BUG=319151
R=tasak@google.com, esprehn, tasak

Review URL: https://codereview.chromium.org/73733003

git-svn-id: svn://svn.chromium.org/blink/trunk@162291 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Introduce ScriptValue::createUndefined

Add ScriptValue::createUndefined static function which returns
a ScriptValue representing an undefined value (not an empty value).

BUG=320984
R=haraken

Review URL: https://codereview.chromium.org/76083002

git-svn-id: svn://svn.chromium.org/blink/trunk@162292 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Verify that video.crossOrigin performs no preflighting.

Verify that a video element CORS fetch doesn't generate a preflight
request and loads the cross-origin resource ok.

R=jochen,kbr
BUG=173727

Review URL: https://codereview.chromium.org/75153002

git-svn-id: svn://svn.chromium.org/blink/trunk@162293 bbb929c8-8fbe-4397-9dbb-9b2b20218538