aura: Destroy the compositor before destroying the backing window.

This was causing linux_aura single-process browser tests to crash since
they don't set up a default X error handler. When the compositor is
shutting down it does a finish and this might try to swap to the X
window.

Also change the windows shutdown ordering to match.

R=ben, enne
BUG=270918

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=245028

Review URL: https://codereview.chromium.org/132473007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@245586 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 245586