BUG=skia:3255
I think this supports everything DM used to, but has completely refactored how
it works to fit the design in the bug.
Configs like "tiles-gpu" are automatically wired up.
I wouldn't suggest looking at this as a diff. There's just a bunch of deleted
files, a few new files, and one new file that shares a name with a deleted file
(DM.cpp).
NOTREECHECKS=true
Review URL: https://codereview.chromium.org/788243008
