Fix ResynthesizerResultProvider's handling of parts.

pkg/analyzer/lib/src/dart/element/handle.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.element_handle;
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/constant/value.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/dart/element/type.dart';
@@ skipping 364 matching lines @@
   bool get isRequired => actualElement.isRequired;
 
   @override
   bool get isSynthetic => actualElement.isSynthetic;
 
   @override
   LibraryElement get library =>
       getAncestor((element) => element is LibraryElement);
 
   @override
+  Source get librarySource => actualElement.librarySource;
+
+  @override
   ElementLocation get location => _location;
 
   @override
   List<ElementAnnotation> get metadata => actualElement.metadata;
 
   @override
   String get name => actualElement.name;
 
   @override
   int get nameLength => actualElement.nameLength;
@@ skipping 718 matching lines @@
 
   @override
   bool get isStatic => actualElement.isStatic;
 
   @override
   DartType get type => actualElement.type;
 
   @override
   DartObject computeConstantValue() => actualElement.computeConstantValue();
 }