Add setPriority to WebURLRequest
R=abarth@chromium.org
CC=jkarlin@chromium.org, japhet@chromium.org

Review URL: https://codereview.chromium.org/338093006

git-svn-id: svn://svn.chromium.org/blink/trunk@176250 bbb929c8-8fbe-4397-9dbb-9b2b20218538