Make UINode's key a String

sky/sdk/lib/widgets/ink_well.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:math' as math;
 import 'dart:sky' as sky;
 
 import '../framework/animation/animated_value.dart';
 import '../framework/animation/curves.dart';
 import '../rendering/box.dart';
@@ skipping 82 matching lines @@
       canvas.clipRect(new Rect.fromSize(size));
       for (InkSplash splash in _splashes)
         splash.paint(canvas);
       canvas.restore();
     }
     super.paint(canvas);
   }
 }
 
 class InkWell extends OneChildRenderObjectWrapper {
-  InkWell({ UINode child, Object key })
-    : super(child: child, key: key);
+  InkWell({ String key, UINode child })
+    : super(key: key, child: child);
 
-  RenderInkWell get root { RenderInkWell result = super.root; return result; }
-
+  RenderInkWell get root => super.root;
   RenderInkWell createNode() => new RenderInkWell();
 }