update AstBuilder to support part of <uri>

pkg/analyzer/lib/src/fasta/ast_builder.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.analyzer.ast_builder;
 
 import 'package:analyzer/analyzer.dart';
 import 'package:analyzer/dart/ast/ast_factory.dart' show AstFactory;
 import 'package:analyzer/dart/ast/standard_ast_factory.dart' as standard;
 import 'package:analyzer/dart/ast/token.dart' show Token, TokenType;
@@ skipping 1403 matching lines @@
     StringLiteral uri = pop();
     List<Annotation> metadata = pop();
     Comment comment = pop();
     directives
         .add(ast.partDirective(comment, metadata, partKeyword, uri, semicolon));
   }
 
   @override
   void endPartOf(Token partKeyword, Token semicolon, bool hasName) {
     debugEvent("PartOf");
-    List<SimpleIdentifier> libraryName = pop();
-    var name = ast.libraryIdentifier(libraryName);
-    StringLiteral uri = null; // TODO(paulberry)
+    var libraryNameOrUri = pop();
+    LibraryIdentifier name;
+    StringLiteral uri;
+    if (libraryNameOrUri is StringLiteral) {
+      uri = libraryNameOrUri;
+    } else {
+      name = ast.libraryIdentifier(libraryNameOrUri);
+    }
     // TODO(paulberry,ahe): seems hacky.  It would be nice if the parser passed
     // in a reference to the "of" keyword.
     var ofKeyword = partKeyword.next;
     List<Annotation> metadata = pop();
     Comment comment = pop();
     directives.add(ast.partOfDirective(
         comment, metadata, partKeyword, ofKeyword, uri, name, semicolon));
   }
 
   @override
@@ skipping 569 matching lines @@
       } else if (identical('var', s)) {
         finalConstOrVarKeyword = token;
       } else if (identical('covariant', s)) {
         covariantKeyword = token;
       } else {
         unhandled("$s", "modifier", token.charOffset, null);
       }
     }
   }
 }