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
[email protected]

Review URL: https://codereview.chromium.org/314113011

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@275638 0039d316-1c4b-4281-b951-d872f2087c98
diff --git a/mojo/mojo.gyp b/mojo/mojo.gyp
index 6fccf62..9786298 100644
--- a/mojo/mojo.gyp
+++ b/mojo/mojo.gyp
@@ -898,8 +898,13 @@
             'mojo_native_viewport_bindings',
           ],
           'sources': [
+            'aura/context_factory_mojo.cc',
+            'aura/context_factory_mojo.h',
             'aura/screen_mojo.cc',
             'aura/screen_mojo.h',
+            'aura/window_tree_host_mojo.cc',
+            'aura/window_tree_host_mojo.h',
+            'aura/window_tree_host_mojo_delegate.h',
           ],
         },
       ],