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

sky/sdk/lib/rendering/paragraph.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 'box.dart';
 import 'object.dart';
 import '../painting/text_style.dart';
 
@@ skipping 136 matching lines @@
   }
 
   double getMinIntrinsicHeight(BoxConstraints constraints) {
     return _getIntrinsicHeight(constraints);
   }
 
   double getMaxIntrinsicHeight(BoxConstraints constraints) {
     return _getIntrinsicHeight(constraints);
   }
 
+  double getDistanceToActualBaseline(TextBaseline baseline) {
+    assert(!needsLayout);
+    _layout(constraints);
+    sky.Element root = _layoutRoot.rootElement;
+    switch (baseline) {
+      case TextBaseline.alphabetic: return root.alphabeticBaseline;
+      case TextBaseline.ideographic: return root.ideographicBaseline;
+    }
+  }
+
   void performLayout() {
     _layout(constraints);
     sky.Element root = _layoutRoot.rootElement;
     // rootElement.width always expands to fill, use maxContentWidth instead.
     size = constraints.constrain(new Size(_applyFloatingPointHack(root.maxContentWidth),
                                           _applyFloatingPointHack(root.height)));
   }
 
   void paint(RenderCanvas canvas) {
     // Ideally we could compute the min/max intrinsic width/height with a
     // non-destructive operation. However, currently, computing these values
     // will destroy state inside the layout root. If that happens, we need to
     // get back the correct state by calling _layout again.
     //
     // TODO(abarth): Make computing the min/max intrinsic width/height a
     //               non-destructive operation.
     _layout(constraints);
     _layoutRoot.paint(canvas);
   }
 
   // we should probably expose a way to do precise (inter-glpyh) hit testing
 
   String debugDescribeSettings(String prefix) {
     String result = '${super.debugDescribeSettings(prefix)}';
     result += '${prefix}inline:\n${inline.toString("$prefix  ")}\n';
     return result;
   }
 }