Use the baseline information exposed by C++ to pipe baseline data through RenderBox.

sky/sdk/lib/rendering/stack.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 'box.dart';
 import 'object.dart';
 
 class StackParentData extends BoxParentData with ContainerParentDataMixin<RenderBox> {
@@ skipping 89 matching lines @@
         height = math.max(height, child.getMaxIntrinsicHeight(constraints));
       }
       child = child.parentData.nextSibling;
     }
     if (!hasNonPositionedChildren)
       return constraints.constrainHeight(double.INFINITY);
     assert(height == constraints.constrainHeight(height));
     return height;
   }
 
+  double getDistanceToActualBaseline(TextBaseline baseline) {
+    return defaultGetDistanceToHighestActualBaseline(baseline);
+  }
+
   void performLayout() {
     bool hasNonPositionedChildren = false;
 
     double width = 0.0;
     double height = 0.0;
 
     RenderBox child = firstChild;
     while (child != null) {
       assert(child.parentData is StackParentData);
       final StackParentData parentData = child.parentData;
@@ skipping 70 matching lines @@
   }
 
   void hitTestChildren(HitTestResult result, { Point position }) {
     defaultHitTestChildren(result, position: position);
   }
 
   void paint(RenderCanvas canvas) {
     defaultPaint(canvas);
   }
 }