Use closure conversion in new dart2js backend.

pkg/compiler/lib/src/tree_ir/optimization/loop_rewriter.dart

Index: pkg/compiler/lib/src/tree_ir/optimization/loop_rewriter.dart
diff --git a/pkg/compiler/lib/src/tree_ir/optimization/loop_rewriter.dart b/pkg/compiler/lib/src/tree_ir/optimization/loop_rewriter.dart
index 182e806f9242e2457417cc8daadbbabe008c771c..c4611570fd63e18dd7b68df0f8b813549b3ac33b 100644
--- a/pkg/compiler/lib/src/tree_ir/optimization/loop_rewriter.dart
+++ b/pkg/compiler/lib/src/tree_ir/optimization/loop_rewriter.dart
@@ -127,4 +127,12 @@ class LoopRewriter extends RecursiveVisitor with PassMixin {
   void visitFunctionExpression(FunctionExpression node) {
     new LoopRewriter().rewrite(node.definition);
   }
+
+  Statement visitSetField(SetField node) {
+    visitExpression(node.object);
+    visitExpression(node.value);
+    node.next = visitStatement(node.next);
+    return node;
+  }
+
 }