Make Analyzer, VM and dart2js accept URI strings as part-of library identifier.

pkg/analyzer/lib/src/generated/parser.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.parser;
 
 import 'dart:collection';
 import "dart:math" as math;
 
 import 'package:analyzer/dart/ast/ast.dart';
@@ skipping 190 matching lines @@
   /**
    * A flag indicating whether the parser is to parse the non-nullable modifier
    * in type names.
    */
   bool _enableNnbd = false;
 
   /**
    * A flag indicating whether the parser is to allow URI's in part-of
    * directives.
    */
-  bool _enableUriInPartOf = false;
+  bool _enableUriInPartOf = true;
 
   /**
    * A flag indicating whether parser is to parse function bodies.
    */
   bool _parseFunctionBodies = true;
 
   /**
    * The next token to be parsed.
    */
   Token _currentToken;
@@ skipping 8294 matching lines @@
    */
   Parser_SyntheticKeywordToken(Keyword keyword, int offset)
       : super(keyword, offset);
 
   @override
   int get length => 0;
 
   @override
   Token copy() => new Parser_SyntheticKeywordToken(keyword, offset);
 }