The 'refresh' pragma directive should be subject to sandboxing.

According to the spec[1], we ought to be limiting meta refreshing based
on the document's sandboxed automatic features browsing context flag.
This patch adds that check into Document::processHttpEquivRefresh.

[1]: http://www.whatwg.org/specs/web-apps/current-work/multipage/semantics.html#attr-meta-http-equiv-refresh

BUG=261603

Review URL: https://chromiumcodereview.appspot.com/19776004

git-svn-id: svn://svn.chromium.org/blink/trunk@154541 bbb929c8-8fbe-4397-9dbb-9b2b20218538