Add debugString to scope.

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

 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library fasta.scope;
 
 import 'builder/builder.dart' show Builder, MixedAccessor;
 
 import 'errors.dart' show internalError;
 
@@ skipping 146 matching lines @@
     if (isModifiable) {
       local[name] = member;
     } else {
       internalError("Can't extend an unmodifiable scope.");
     }
   }
 
   void forEach(f(String name, Builder member)) {
     local.forEach(f);
   }
+
+  String get debugString {
+    StringBuffer buffer = new StringBuffer();
+    int nestingLevel = writeOn(buffer);
+    for (int i = nestingLevel; i >= 0; i--) {
+      buffer.writeln("${'  ' * i}}");
+    }
+    return "$buffer";
+  }
+
+  int writeOn(StringSink sink) {
+    int nestingLevel = (parent?.writeOn(sink) ?? -1) + 1;
+    String indent = "  " * nestingLevel;
+    sink.writeln("$indent{");
+    local.forEach((String name, Builder member) {
+      sink.writeln("$indent  $name");
+    });
+    setters.forEach((String name, Builder member) {
+      sink.writeln("$indent  $name=");
+    });
+    return nestingLevel;
+  }
 }
 
 abstract class ProblemBuilder extends Builder {
   final String name;
 
   final Builder builder;
 
   ProblemBuilder(this.name, this.builder, int charOffset, Uri fileUri)
       : super(null, charOffset, fileUri);
 
@@ skipping 37 matching lines @@
 
   String get message => "Access error: '$name'.";
 }
 
 class AmbiguousBuilder extends ProblemBuilder {
   AmbiguousBuilder(String name, Builder builder, int charOffset, Uri fileUri)
       : super(name, builder, charOffset, fileUri);
 
   String get message => "Duplicated named: '$name'.";
 }