Update test case to cover escaping while processing image URLs.

Depends on the change in https://codereview.chromium.org/24662002/, prior to which this will fail as the full fragment is not copied.

BUG=297718
R=tony@chromium.org

Review URL: https://chromiumcodereview.appspot.com/24530004

git-svn-id: svn://svn.chromium.org/blink/trunk@158547 bbb929c8-8fbe-4397-9dbb-9b2b20218538