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

sky/sdk/lib/rendering/flex.dart

Index: sky/sdk/lib/rendering/flex.dart
diff --git a/sky/sdk/lib/rendering/flex.dart b/sky/sdk/lib/rendering/flex.dart
index e4b7422a3c055b52ad160e231c7504a62af40372..5919ab1d72fdfc04dba1fa4490ce39db8e85b55c 100644
--- a/sky/sdk/lib/rendering/flex.dart
+++ b/sky/sdk/lib/rendering/flex.dart
@@ -246,11 +246,10 @@ class RenderFlex extends RenderBox with ContainerRenderObjectMixin<RenderBox, Fl
       childSize: (c, innerConstraints) => c.getMaxIntrinsicHeight(innerConstraints));
   }
 
-  double getDistanceToActualBaseline(TextBaseline baseline) {
-    assert(!needsLayout);
+  double computeDistanceToActualBaseline(TextBaseline baseline, RenderObject client) {
     if (_direction == FlexDirection.horizontal)
-      return defaultGetDistanceToHighestActualBaseline(baseline);
-    return defaultGetDistanceToFirstActualBaseline(baseline);
+      return defaultComputeDistanceToHighestActualBaseline(baseline, client);
+    return defaultComputeDistanceToFirstActualBaseline(baseline, client);
   }
 
   int _getFlex(RenderBox child) {