Fix for ScopeBuilder[] - look into setters too.

pkg/front_end/lib/src/fasta/scope.dart

Index: pkg/front_end/lib/src/fasta/scope.dart
diff --git a/pkg/front_end/lib/src/fasta/scope.dart b/pkg/front_end/lib/src/fasta/scope.dart
index dec63216a427478f30dc12e9ea83b2b5bfd1a504..54356f0ccb9e558536daf7c91d642671a8c8d38a 100644
--- a/pkg/front_end/lib/src/fasta/scope.dart
+++ b/pkg/front_end/lib/src/fasta/scope.dart
@@ -280,7 +280,9 @@ class ScopeBuilder {
     scope.setters[name] = builder;
   }
 
-  Builder operator [](String name) => scope.local[name];
+  Builder operator [](String name) {
+    return scope.local[name] ?? scope.setters[name];
+  }
 }
 
 abstract class ProblemBuilder extends Builder {