Add new "resize" event to HTMLMediaElement.
This event was added in http://html5.org/r/8347 and so I'm claiming "trivial" for the blink web-facing policy (since this is a minor change to a shipping spec that improves compliance to the standard).

TESTED=./webkit/tools/layout_tests/run_webkit_tests.sh -f --debug media http/tests/media
BUG=328140

Review URL: https://codereview.chromium.org/103913010

git-svn-id: svn://svn.chromium.org/blink/trunk@163900 bbb929c8-8fbe-4397-9dbb-9b2b20218538