Wires up painting of layerless children

BUG=none
TEST=covered by tests.
R=ben@chromium.org

Review URL: https://codereview.chromium.org/102313002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@238453 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 238453