Implement getter/setter in PaintInfo::rect.

Signed-off-by: Adenilson Cavalcanti <cavalcantii@gmail.com>

BUG=266575

Review URL: https://chromiumcodereview.appspot.com/23494007

git-svn-id: svn://svn.chromium.org/blink/trunk@156859 bbb929c8-8fbe-4397-9dbb-9b2b20218538