Make popup menus line up to their baseline per the Material spec.

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:sky' as sky;
 
 import 'package:vector_math/vector_math.dart';
 
 import '../painting/text_style.dart';
 import '../rendering/block.dart';
@@ skipping 236 matching lines @@
   RenderShrinkWrapWidth createNode() => new RenderShrinkWrapWidth();
 
   void syncRenderObject(ShrinkWrapWidth old) {
     super.syncRenderObject(old);
     root.stepWidth = stepWidth;
     root.stepHeight = stepHeight;
   }
 
 }
 
+class Baseline extends OneChildRenderObjectWrapper {
+
+  Baseline({
+    String key,
+    this.baseline, // in pixels
+    this.baselineType: TextBaseline.alphabetic,
+    Widget child
+  }): super(key: key, child: child);
+
+  RenderBaseline get root => super.root;
+
+  final double baseline;
+  final TextBaseline baselineType;
+
+  RenderBaseline createNode() => new RenderBaseline(baseline: baseline, baselineType: baselineType);
+
+  void syncRenderObject(Baseline old) {
+    super.syncRenderObject(old);
+    root.baseline = baseline;
+    root.baselineType = baselineType;
+  }
+
+}
+
 class SizeObserver extends OneChildRenderObjectWrapper {
 
   SizeObserver({ String key, this.callback, Widget child })
     : super(key: key, child: child);
 
   RenderSizeObserver get root => super.root;
   final SizeChangedCallback callback;
 
   RenderSizeObserver createNode() => new RenderSizeObserver(callback: callback);
 
@@ skipping 238 matching lines @@
   }
 
   void remove() {
     RenderObjectWrapper ancestor = findAncestor(RenderObjectWrapper);
     assert(ancestor is RenderObjectWrapper);
     ancestor.detachChildRoot(this);
     super.remove();
   }
 
 }