Update a stale comment in RenderLayer.
Update a stale comment in RenderLayer.

The CompositedLayerMapping::paintIntoLayer method is no more, point to
the methods that do what it used to do.

R=jchaffraix@chromium.org

Review URL: https://codereview.chromium.org/292743012

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@174528 bbb929c8-8fbe-4397-9dbb-9b2b20218538

primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs