Implement document.currentScript http://www.whatwg.org/specs/web-apps/current-work/multipage/dom.html#dom-document-currentscript document.currentScript reflects the script that is currently being executed. BUG=240876 Review URL: https://chromiumcodereview.appspot.com/14852011 git-svn-id: svn://svn.chromium.org/blink/trunk@152230 bbb929c8-8fbe-4397-9dbb-9b2b20218538 LayoutTests/fast/dom/Document/do