Add an AspectRatio widget for doing proportional height sizing

sky/sdk/lib/widgets/basic.dart

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 import 'dart:async';
 import 'dart:sky' as sky;
 
 import 'package:vector_math/vector_math.dart';
 
 import 'package:sky/mojo/asset_bundle.dart';
@@ skipping 199 matching lines @@
 
   RenderConstrainedBox createNode() => new RenderConstrainedBox(additionalConstraints: constraints);
   RenderConstrainedBox get root => super.root;
 
   void syncRenderObject(ConstrainedBox old) {
     super.syncRenderObject(old);
     root.additionalConstraints = constraints;
   }
 }
 
+class AspectRatio extends OneChildRenderObjectWrapper {
+  AspectRatio({ String key, this.aspectRatio, Widget child })
+    : super(key: key, child: child);
+
+  final double aspectRatio;
+
+  RenderAspectRatio createNode() => new RenderAspectRatio(aspectRatio: aspectRatio);
+  RenderAspectRatio get root => super.root;
+
+  void syncRenderObject(AspectRatio old) {
+    super.syncRenderObject(old);
+    root.aspectRatio = aspectRatio;
+  }
+}
+
 class ShrinkWrapWidth extends OneChildRenderObjectWrapper {
   ShrinkWrapWidth({ String key, this.stepWidth, this.stepHeight, Widget child })
     : super(key: key, child: child);
 
   final double stepWidth;
   final double stepHeight;
 
   RenderShrinkWrapWidth createNode() => new RenderShrinkWrapWidth();
   RenderShrinkWrapWidth get root => super.root;
 
@@ skipping 339 matching lines @@
   }
 
   void remove() {
     RenderObjectWrapper ancestor = findAncestorRenderObjectWrapper();
     assert(ancestor is RenderObjectWrapper);
     assert(ancestor.root == root.parent);
     ancestor.detachChildRoot(this);
     super.remove();
   }
 }