Re-enable compositing for will-change:top/left/bottom/right

This re-enables compositing for will-change:top/left/bottom/right, for
elements that already have a self-painting RenderLayer.

BUG=371352

Review URL: https://codereview.chromium.org/286823003

git-svn-id: svn://svn.chromium.org/blink/trunk@174036 bbb929c8-8fbe-4397-9dbb-9b2b20218538