Change Link to List in FunctionSignature.

pkg/compiler/lib/src/dart_backend/placeholder_collector.dart

Index: pkg/compiler/lib/src/dart_backend/placeholder_collector.dart
diff --git a/pkg/compiler/lib/src/dart_backend/placeholder_collector.dart b/pkg/compiler/lib/src/dart_backend/placeholder_collector.dart
index 04a7b7c9263413866084fc7ef5fd9d266d45dd2f..e32f4a5a91e15a1955ace9ca78c633eedce3adae 100644
--- a/pkg/compiler/lib/src/dart_backend/placeholder_collector.dart
+++ b/pkg/compiler/lib/src/dart_backend/placeholder_collector.dart
@@ -503,7 +503,7 @@ class PlaceholderCollector extends Visitor {
       // }
       // Do not forget to rename them as well.
       FunctionElement constructorFunction = constructor;
-      Link<Element> optionalParameters =
+      List<Element> optionalParameters =
           constructorFunction.functionSignature.optionalParameters;
       for (final argument in send.argumentsNode) {
         NamedArgument named = argument.asNamedArgument();