Include debug name in GraphicsLayerDebugInfo.

This should let us kill a bunch of plumbing. Once cc starts
using takeDebugInfoFor (and stops using the debugName
codepath), WebGraphicsLayerClient's debugName and
takeDebugInfo methods can be removed.

R=jamesr@chromium.org
BUG=None

Review URL: https://codereview.chromium.org/135473002

git-svn-id: svn://svn.chromium.org/blink/trunk@165005 bbb929c8-8fbe-4397-9dbb-9b2b20218538