Add the 'docRange' property and use it to compute documentation comment.

pkg/analyzer/lib/src/generated/testing/ast_factory.dart

 // Copyright (c) 2014, 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 engine.testing.ast_factory;
 
 import 'package:analyzer/src/generated/ast.dart';
 import 'package:analyzer/src/generated/element.dart';
 import 'package:analyzer/src/generated/scanner.dart';
 import 'package:analyzer/src/generated/testing/token_factory.dart';
@@ skipping 359 matching lines @@
           type,
           identifier3(identifier));
 
   static DeclaredIdentifier declaredIdentifier3(String identifier) =>
       declaredIdentifier2(Keyword.VAR, null, identifier);
 
   static DeclaredIdentifier declaredIdentifier4(
           TypeName type, String identifier) =>
       declaredIdentifier2(null, type, identifier);
 
+  static Comment documentationComment(
+      List<Token> tokens, List<CommentReference> references) {
+    return new Comment(tokens, CommentType.DOCUMENTATION, references);
+  }
+
   static DoStatement doStatement(Statement body, Expression condition) =>
       new DoStatement(
           TokenFactory.tokenFromKeyword(Keyword.DO),
           body,
           TokenFactory.tokenFromKeyword(Keyword.WHILE),
           TokenFactory.tokenFromType(TokenType.OPEN_PAREN),
           condition,
           TokenFactory.tokenFromType(TokenType.CLOSE_PAREN),
           TokenFactory.tokenFromType(TokenType.SEMICOLON));
 
@@ skipping 856 matching lines @@
           expression,
           TokenFactory.tokenFromType(TokenType.SEMICOLON));
 
   static YieldStatement yieldStatement(Expression expression) =>
       new YieldStatement(
           TokenFactory.tokenFromTypeAndString(TokenType.IDENTIFIER, "yield"),
           null,
           expression,
           TokenFactory.tokenFromType(TokenType.SEMICOLON));
 }