RenderLayer and RenderLayerClipper should not be friends

This change moves backgroundClipRect and
parentClipRect to break the bad friendness.

BUG=307169

Review URL: https://codereview.chromium.org/126193002

git-svn-id: svn://svn.chromium.org/blink/trunk@164755 bbb929c8-8fbe-4397-9dbb-9b2b20218538