Moves common view_manager related aura files to mojo/aura

Moves common view_manager related aura files to mojo/aura

I'm going to use these files in other examples. I refactored the code slightly to update compositor via a delegate. This way the code can easily (hopefully) be used by view_manager_lib related code.

I'm also making aura::Env extend base::SupportsUserData so that
consumers can add arbitrary key/value pairs to Env.

BUG=365012
TEST=none
R=ben@chromium.org

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=275638

[Ben Goodger (Google), 2014-06-06 17:53:27]

lgtm

[sky, 2014-06-06 17:54:12]

The CQ bit was checked by sky@chromium.org

[commit-bot: I haz the power, 2014-06-06 17:55:52]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/sky@chromium.org/314113011/20001

[commit-bot: I haz the power, 2014-06-07 05:59:50]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  win_chromium_rel on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/win_chromium_rel/buil...)

[commit-bot: I haz the power, 2014-06-07 08:17:49]

Change committed as 275638