InstantExtended: update tests for Instant Extended (part 5).

Turning on InstantExtended by default exposes some flakiness in the url rewrite
browser test. Change the test to a unit test to remove flakiness. Also update
OWNERS file to allow anyone to change the unit test (since anyone can already
change the .cc/.h files + the browser tests).

(Note that this is split off from http://crrev.com/24733003.)

BUG=297915
R=jered@chromium.org, sky@chromium.org

Review URL: https://codereview.chromium.org/59493009

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@234956 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 234956