Adds a porting layer so aura can be made to work with mus
This introduces WindowPort and the single concrete implementation of
it WindowPortAura. WindowPort contains the set of functions needed to
get aura to work with mus. A new constructor is added to Window and
WindowTreeNhost that can be used to specify an explicit
WindowPort. This is not the common case though, the common case is to
use a constructor that does not take a WindowPort, in which case a
WindowPort is created using a callback specified at the time of
creating Env.
BUG=659155
TEST=covered by existing tests
sadrul@chromium.org
Review-Url: https://codereview.chromium.org/2446893005
Cr-Commit-Position: refs/heads/master@{#427750}
14 files changed