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

sky/sdk/lib/rendering/block.dart

Index: sky/sdk/lib/rendering/block.dart
diff --git a/sky/sdk/lib/rendering/block.dart b/sky/sdk/lib/rendering/block.dart
index 4d163db4a29001d57e482ec699dc52da7ed81dc0..ff840446b1a6ef4a4798b5621bae9b176da4d067 100644
--- a/sky/sdk/lib/rendering/block.dart
+++ b/sky/sdk/lib/rendering/block.dart
@@ -77,6 +77,10 @@ class RenderBlock extends RenderBox with ContainerRenderObjectMixin<RenderBox, B
     return _getIntrinsicHeight(constraints);
   }
 
+  double getDistanceToActualBaseline(TextBaseline baseline) {
+    return defaultGetDistanceToFirstActualBaseline(baseline);
+  }
+
   void performLayout() {
     assert(constraints is BoxConstraints);
     double width = constraints.constrainWidth(constraints.maxWidth);