dart2dart Fix renaming of top-level setters.

lib/compiler/implementation/dart_backend/placeholder_collector.dart

Index: lib/compiler/implementation/dart_backend/placeholder_collector.dart
diff --git a/lib/compiler/implementation/dart_backend/placeholder_collector.dart b/lib/compiler/implementation/dart_backend/placeholder_collector.dart
index 52322394425f3b619685f9beda0fcaab0852d93e..9c4d614a767db57974c71055974545ef4d29bc0c 100644
--- a/lib/compiler/implementation/dart_backend/placeholder_collector.dart
+++ b/lib/compiler/implementation/dart_backend/placeholder_collector.dart
@@ -303,6 +303,9 @@ class PlaceholderCollector extends AbstractVisitor {
     if (element !== null) {
       if (element.isInstanceMember()) {
         tryMakePrivateIdentifier(send.selector.asIdentifier());
+      } else if (element.isTopLevel()) {
+        assert(element is VariableElement || element.isSetter());
+        makeElementPlaceholder(send.selector, element);
       } else {
         assert(send.selector is Identifier);
         tryMakeLocalPlaceholder(element, send.selector);