Add parser support for using a URI in a part-of directive

pkg/analyzer/lib/src/generated/testing/ast_test_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 analyzer.src.generated.testing.ast_test_factory;
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/token.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/src/dart/ast/ast.dart';
@@ skipping 955 matching lines @@
   static PartOfDirective partOfDirective(LibraryIdentifier libraryName) =>
       partOfDirective2(new List<Annotation>(), libraryName);
 
   static PartOfDirective partOfDirective2(
           List<Annotation> metadata, LibraryIdentifier libraryName) =>
       new PartOfDirective(
           null,
           metadata,
           TokenFactory.tokenFromKeyword(Keyword.PART),
           TokenFactory.tokenFromString("of"),
+          null,
           libraryName,
           TokenFactory.tokenFromType(TokenType.SEMICOLON));
 
   static DefaultFormalParameter positionalFormalParameter(
           NormalFormalParameter parameter, Expression expression) =>
       new DefaultFormalParameter(
           parameter,
           ParameterKind.POSITIONAL,
           expression == null ? null : TokenFactory.tokenFromType(TokenType.EQ),
           expression);
@@ skipping 299 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));
 }