Add some new reftests which cover filter primitive subregion when scaled by page
zoom, or by hidpi. They should all be passing. I'm landing them to prevent
introducing regressions with upcoming patches (likely by me :) ).  Note that
page zoom applied to filter primitive subregion doesn't seem to be working in
the raster (non-hw) path. See http://crbug.com/335282.

R=fmalita

Review URL: https://codereview.chromium.org/136473005

git-svn-id: svn://svn.chromium.org/blink/trunk@165259 bbb929c8-8fbe-4397-9dbb-9b2b20218538