Make test script take-focus-from-iframe.html to DOM only test

This patch changes  take-focus-from-iframe.html  to DOM only test rather than
pixel test for ease of test script maintance.

BUG=n/a
TEST=LayoutTests/fast/frames/take-focus-from-iframe.html

Review URL: https://codereview.chromium.org/330653007

git-svn-id: svn://svn.chromium.org/blink/trunk@176822 bbb929c8-8fbe-4397-9dbb-9b2b20218538