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pre-cursor to moving Chrome OS + Aura away from legacy GTK+X11 dibs. Now, we
have just:
- Windows style dibs
- POSIX style dibs
- Legacy GTK+X11 style dibs.

There's some ifdef hoops that will be removed in a follow-up CL when
Chrome OS + Aura will be moved away from legacy GTK+X11 dibs and on to POSIX
dibs.

BUG=147622
Review URL: https://codereview.chromium.org/13582008

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@192629 0039d316-1c4b-4281-b951-d872f2087c98