Begin hooking up Fasta to analyzer parser tests.

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

Index: pkg/front_end/lib/src/fasta/builder/scope.dart
diff --git a/pkg/front_end/lib/src/fasta/builder/scope.dart b/pkg/front_end/lib/src/fasta/builder/scope.dart
index c0d17e6990831bff6d017fb21047fb776a879e0e..015045775643023ba99a29c30a7ead42ae2fc9e4 100644
--- a/pkg/front_end/lib/src/fasta/builder/scope.dart
+++ b/pkg/front_end/lib/src/fasta/builder/scope.dart
@@ -12,10 +12,15 @@ import '../errors.dart' show
     internalError;
 
 class Scope {
+  /// Names declared in this scope.
   final Map<String, Builder> local;
 
+  /// The scope that this scope is nested within, or `null` if this is the top
+  /// level scope.
   final Scope parent;
 
+  /// Indicates whether an attempt to declare new names in this scope should
+  /// succeed.
   final bool isModifiable;
 
   Scope(this.local, this.parent, {this.isModifiable: true});