Port pixelzoomer.js/css to ct-results-comparison.

This broke when I changed the results comparison to use polymer components.
This isn't 100% the same as the old pixelzoomer code. I took this as an
opportunity to simplify it.

Also, change the 4-space indent to 2-space indent and replace
endOfMicroTask calls with requestAnimationFrame to match the rest of
the codebase.

NOTRY=true

Review URL: https://codereview.chromium.org/403983002

git-svn-id: svn://svn.chromium.org/blink/trunk@178536 bbb929c8-8fbe-4397-9dbb-9b2b20218538