Deflake editing/selection/4960116.html by making it text-only.

This test has flaky image failures depending on whether the cursor is
blinked on or blinked off. It also has flaky text failures depending
on whether "caret:" is output.

This is a crash regression test, so the exact whereabouts of the
cursor aren't particularly interesting. I'm making this dumpAsText.

BUG=365917,341682
R=tkent@chromium.org

Review URL: https://codereview.chromium.org/248563002

git-svn-id: svn://svn.chromium.org/blink/trunk@172307 bbb929c8-8fbe-4397-9dbb-9b2b20218538