Mojo: Abstract out the endpoints of MessagePipes.

This will allow us to plug in different kinds of endpoints, in particular,
non-local endpoints (so that MessagePipes can be cross-process, with, e.g., a
socket as transport).

R=darin

Review URL: https://codereview.chromium.org/27060003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@228815 0039d316-1c4b-4281-b951-d872f2087c98
Enable GPU Control lists on Mac.

This is the Mac follow-up to http://crrev.com/228530.

TBR=zmo, vangelis, jcivelli
BUG=295799

Review URL: https://codereview.chromium.org/27332002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@228816 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 228815
SVN changes up to revision 228816