Introduce Scaffold to Sky framework

sky/framework/components/drawer.dart

Index: sky/framework/components/drawer.dart
diff --git a/sky/framework/components/drawer.dart b/sky/framework/components/drawer.dart
index 9020c2da702f871a201f7c29c76a6eb71d510772..20045479735374bf1f554ac20f468f3f43cb9511 100644
--- a/sky/framework/components/drawer.dart
+++ b/sky/framework/components/drawer.dart
@@ -76,13 +76,10 @@ class DrawerController {
 }
 
 class Drawer extends AnimatedComponent {
+  // TODO(abarth): We need a better way to become a container for absolutely
+  // positioned elements.
   static final Style _style = new Style('''
-    position: absolute;
-    top: 0;
-    left: 0;
-    bottom: 0;
-    right: 0;'''
-  );
+    transform: translateX(0);''');
 
   static final Style _maskStyle = new Style('''
     background-color: black;