[WEB-16445] When create a missing imported library/part, add the edit once.

pkg/analysis_server/lib/src/services/correction/fix_internal.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 analysis_server.src.services.correction.fix_internal;
 
 import 'dart:collection';
 
 import 'package:analysis_server/edit/fix/fix_core.dart';
 import 'package:analysis_server/edit/fix/fix_dart.dart';
@@ skipping 904 matching lines @@
   void _addFix_createImportUri() {
     if (node is SimpleStringLiteral && node.parent is ImportDirective) {
       ImportDirective importDirective = node.parent;
       Source source = importDirective.source;
       if (source != null) {
         String file = source.fullName;
         if (isAbsolute(file)) {
           String libName = removeEnd(source.shortName, '.dart');
           libName = libName.replaceAll('_', '.');
           SourceEdit edit = new SourceEdit(0, 0, 'library $libName;$eol$eol');
-          change.addEdit(file, -1, edit);
           doSourceChange_addSourceEdit(change, context, source, edit);
         }
         _addFix(DartFixKind.CREATE_FILE, [file]);
       }
     }
   }
 
   void _addFix_createLocalVariable() {
     if (node is! SimpleIdentifier) {
       return;
@@ skipping 184 matching lines @@
   }
 
   void _addFix_createPartUri() {
     if (node is SimpleStringLiteral && node.parent is PartDirective) {
       PartDirective partDirective = node.parent;
       Source source = partDirective.source;
       if (source != null) {
         String file = source.fullName;
         String libName = unitLibraryElement.name;
         SourceEdit edit = new SourceEdit(0, 0, 'part of $libName;$eol$eol');
-        change.addEdit(file, -1, edit);
         doSourceChange_addSourceEdit(change, context, source, edit);
         _addFix(DartFixKind.CREATE_FILE, [file]);
       }
     }
   }
 
   void _addFix_illegalAsyncReturnType() {
     InterfaceType futureType = context.typeProvider.futureType;
     String futureTypeCode = utils.getTypeSource(futureType, librariesToImport);
     // prepare the existing type
@@ skipping 1399 matching lines @@
 /**
  * Describes the location for a newly created [FieldDeclaration].
  */
 class _FieldLocation {
   final String prefix;
   final int offset;
   final String suffix;
 
   _FieldLocation(this.prefix, this.offset, this.suffix);
 }