Don't update offsets for elements of 'part' and 'part of' directives.

pkg/analyzer/lib/src/task/incremental_element_builder.dart

 // Copyright (c) 2015, 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.task.incremental_element_builder;
 
 import 'dart:collection';
 
 import 'package:analyzer/src/generated/ast.dart';
 import 'package:analyzer/src/generated/element.dart';
@@ skipping 144 matching lines @@
     if (node is TopLevelVariableDeclaration) {
       VariableDeclarationList variableList = node.variables;
       if (variableList != null) {
         for (VariableDeclaration variable in variableList.variables) {
           TopLevelVariableElement element = variable.element;
           elements.add(element);
           elements.add(element.getter);
           elements.add(element.setter);
         }
       }
+    } else if (node is PartDirective || node is PartOfDirective) {
     } else if (node is Directive && node.element != null) {
       elements.add(node.element);
     } else if (node is Declaration && node.element != null) {
       Element element = node.element;
       elements.add(element);
       if (element is PropertyAccessorElement) {
         elements.add(element.variable);
       }
     }
     return elements;
@@ skipping 107 matching lines @@
     }
     int oldOffset = element.nameOffset;
     int newOffset = map[oldOffset];
     assert(newOffset != null);
     (element as ElementImpl).nameOffset = newOffset;
     if (element is! LibraryElement) {
       super.visitElement(element);
     }
   }
 }