Move reftests from fast/dom/HTMLDialogElement/ to dialog/

These tests are slow and aren't testing just DOM but end-to-end rendering.
This should make fast/dom/HTMLDialogElement at least 50% faster.

NOTRY=true

Review URL: https://chromiumcodereview.appspot.com/18751002

git-svn-id: svn://svn.chromium.org/blink/trunk@153658 bbb929c8-8fbe-4397-9dbb-9b2b20218538