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

sky/sdk/lib/rendering/stack.dart

Index: sky/sdk/lib/rendering/stack.dart
diff --git a/sky/sdk/lib/rendering/stack.dart b/sky/sdk/lib/rendering/stack.dart
index 72a7cb62665d6fdda0596cc108c47d02d3660ba5..a3efa186e095e854537c9925bd22750ba3fa88c9 100644
--- a/sky/sdk/lib/rendering/stack.dart
+++ b/sky/sdk/lib/rendering/stack.dart
@@ -107,6 +107,10 @@ class RenderStack extends RenderBox with ContainerRenderObjectMixin<RenderBox, S
     return height;
   }
 
+  double getDistanceToActualBaseline(TextBaseline baseline) {
+    return defaultGetDistanceToHighestActualBaseline(baseline);
+  }
+
   void performLayout() {
     bool hasNonPositionedChildren = false;