Don't anti-alias backgrounds of images.

This fixes a pixel bleed issue on very high-DPI screens.

BUG=423834

Review URL: https://codereview.chromium.org/711163002

git-svn-id: svn://svn.chromium.org/blink/trunk@185161 bbb929c8-8fbe-4397-9dbb-9b2b20218538