[WIP] Adding Element.closest() API

Implementing Element.closest() API according to specs
https://dom.spec.whatwg.org/#dom-element-closest

This API will parse selectors and if fails then throw SyntaxError
else return closest ancestor that matches selectors
if there is no ancestor that matches selectors, it will
return nullptr.

Blink-Dev Intent to Implement and ship Link :
https://groups.google.com/a/chromium.org/forum/#!topic/blink-dev/yk_Fo6hyvb8

WebKit Change: http://trac.webkit.org/changeset/174324

BUG=422731
R=habib.virji@samsung.com

Review URL: https://codereview.chromium.org/704733002

git-svn-id: svn://svn.chromium.org/blink/trunk@184946 bbb929c8-8fbe-4397-9dbb-9b2b20218538