Prepare for separate setter scope.

pkg/front_end/lib/src/fasta/builder/procedure_builder.dart

Index: pkg/front_end/lib/src/fasta/builder/procedure_builder.dart
diff --git a/pkg/front_end/lib/src/fasta/builder/procedure_builder.dart b/pkg/front_end/lib/src/fasta/builder/procedure_builder.dart
index eef79154e907565eb7e07f28f57c9c5187e37c0e..446ed241ed96d2a8aa04bba0daee99a4b3511835 100644
--- a/pkg/front_end/lib/src/fasta/builder/procedure_builder.dart
+++ b/pkg/front_end/lib/src/fasta/builder/procedure_builder.dart
@@ -72,7 +72,7 @@ abstract class ProcedureBuilder<T extends TypeBuilder> extends MemberBuilder {
         local[formal.name] = formal;
       }
     }
-    return new Scope(local, parent, isModifiable: false);
+    return new Scope(local, null, parent, isModifiable: false);
   }
 
   /// This scope doesn't correspond to any scope specified in the Dart
@@ -84,6 +84,6 @@ abstract class ProcedureBuilder<T extends TypeBuilder> extends MemberBuilder {
     for (TypeVariableBuilder variable in typeVariables) {
       local[variable.name] = variable;
     }
-    return new Scope(local, parent, isModifiable: false);
+    return new Scope(local, null, parent, isModifiable: false);
   }
 }