Add support for assert statements with messages to the analyzer.

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 28 matching lines @@
           arguments);
 
   static ArgumentList argumentList([List<Expression> arguments]) =>
       new ArgumentList(TokenFactory.tokenFromType(TokenType.OPEN_PAREN),
           arguments, TokenFactory.tokenFromType(TokenType.CLOSE_PAREN));
 
   static AsExpression asExpression(Expression expression, TypeName type) =>
       new AsExpression(
           expression, TokenFactory.tokenFromKeyword(Keyword.AS), type);
 
-  static AssertStatement assertStatement(Expression condition) =>
-      new AssertStatement(
+  static AssertStatement assertStatement(Expression condition,
+          [Expression message]) =>
+      new AssertStatement.withOptionalMessage(
           TokenFactory.tokenFromKeyword(Keyword.ASSERT),
           TokenFactory.tokenFromType(TokenType.OPEN_PAREN),
           condition,
+          message == null ? null : TokenFactory.tokenFromType(TokenType.COMMA),
+          message,
           TokenFactory.tokenFromType(TokenType.CLOSE_PAREN),
           TokenFactory.tokenFromType(TokenType.SEMICOLON));
 
   static AssignmentExpression assignmentExpression(Expression leftHandSide,
           TokenType operator, Expression rightHandSide) =>
       new AssignmentExpression(
           leftHandSide, TokenFactory.tokenFromType(operator), rightHandSide);
 
   static BlockFunctionBody asyncBlockFunctionBody(
           [List<Statement> statements]) =>
@@ skipping 1182 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));
 }