Basic Sky shell for iOS targets

sky/shell/ios/sky_surface.h

Index: sky/shell/ios/sky_surface.h
diff --git a/sky/engine/core/painting/DrawLooper.idl b/sky/shell/ios/sky_surface.h
similarity index 72%
copy from sky/engine/core/painting/DrawLooper.idl
copy to sky/shell/ios/sky_surface.h
index 8fbda9d1f82e171b595c0d03c1eb0dc652f24f23..bb65f2d85989b3f844ea26cfcc77d04f0d49ea6e 100644
--- a/sky/engine/core/painting/DrawLooper.idl
+++ b/sky/shell/ios/sky_surface.h
@@ -2,5 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-interface DrawLooper {
-};
+#import <UIKit/UIKit.h>
+
+@interface SkySurface : UIView
+
+@end