Basic Sky shell for iOS targets

sky/shell/ios/sky_app_delegate.h

Index: sky/shell/ios/sky_app_delegate.h
diff --git a/sky/compositor/rasterizer.cc b/sky/shell/ios/sky_app_delegate.h
similarity index 54%
copy from sky/compositor/rasterizer.cc
copy to sky/shell/ios/sky_app_delegate.h
index e0eb2d5c189c617e86582c3b774a6fa35e23af65..9103726971e97a9750cf91814095762e7c267d82 100644
--- a/sky/compositor/rasterizer.cc
+++ b/sky/shell/ios/sky_app_delegate.h
@@ -2,14 +2,10 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#include "sky/compositor/rasterizer.h"
+#import <UIKit/UIKit.h>
 
-namespace sky {
+@interface SkyAppDelegate : UIResponder<UIApplicationDelegate>
 
-Rasterizer::Rasterizer() {
-}
+@property(strong, nonatomic) UIWindow* window;
 
-Rasterizer::~Rasterizer() {
-}
-
-}  // namespace sky
+@end