Merge kernel closure conversion into the Dart SDK

pkg/kernel/lib/visitor.dart

Index: pkg/kernel/lib/visitor.dart
diff --git a/pkg/kernel/lib/visitor.dart b/pkg/kernel/lib/visitor.dart
index c48f0d425a7165975a4480578058dd134c21b8e2..bbefd951e7e01c08f8e2dfe07ed5ab402ac9e0b9 100644
--- a/pkg/kernel/lib/visitor.dart
+++ b/pkg/kernel/lib/visitor.dart
@@ -235,9 +235,7 @@ class MemberReferenceVisitor<R> {
 }
 
 class Visitor<R> extends TreeVisitor<R>
-    implements
-        DartTypeVisitor<R>,
-        MemberReferenceVisitor<R> {
+    implements DartTypeVisitor<R>, MemberReferenceVisitor<R> {
   /// The catch-all case, except for references.
   R defaultNode(Node node) => null;
   R defaultTreeNode(TreeNode node) => defaultNode(node);