Rename Rasterize to Paint in the UI. This decreases confusion
around what paint costs are on mobile.

BUG=305860
R=caseq

Review URL: https://codereview.chromium.org/68103021

git-svn-id: svn://svn.chromium.org/blink/trunk@162336 bbb929c8-8fbe-4397-9dbb-9b2b20218538