Fix ResynthesizerResultProvider's handling of parts.

pkg/analyzer/lib/src/dart/element/element.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.dart.element.element;
 
 import 'dart:collection';
 import 'dart:math' show min;
 
 import 'package:analyzer/dart/ast/ast.dart';
@@ skipping 2849 matching lines @@
   bool get isResynthesized => enclosingUnit?.resynthesizerContext != null;
 
   @override
   bool get isSynthetic => hasModifier(Modifier.SYNTHETIC);
 
   @override
   LibraryElement get library =>
       getAncestor((element) => element is LibraryElement);
 
   @override
+  Source get librarySource => library?.source;
+
+  @override
   ElementLocation get location {
     if (_cachedLocation == null) {
       if (library == null) {
         return new ElementLocationImpl.con1(this);
       }
       _cachedLocation = new ElementLocationImpl.con1(this);
     }
     return _cachedLocation;
   }
 
@@ skipping 3646 matching lines @@
   @override
   int get nameLength => displayName != null ? displayName.length : 0;
 
   @override
   int get nameOffset => -1;
 
   @override
   Source get source => null;
 
   @override
+  Source get librarySource => null;
+
+  @override
   DartType get type => DynamicTypeImpl.instance;
 
   @override
   CompilationUnit get unit => null;
 
   @override
   accept(ElementVisitor visitor) => visitor.visitMultiplyDefinedElement(this);
 
   @override
   String computeDocumentationComment() => null;
@@ skipping 1896 matching lines @@
 
   @override
   void visitElement(Element element) {
     int offset = element.nameOffset;
     if (offset != -1) {
       map[offset] = element;
     }
     super.visitElement(element);
   }
 }