Issue 26764. Insert required imports in the correct sorting order.

pkg/analysis_server/test/services/correction/assist_test.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 test.services.correction.assist;
 
 import 'dart:async';
 
 import 'package:analysis_server/plugin/edit/assist/assist_core.dart';
 import 'package:analysis_server/plugin/protocol/protocol.dart';
@@ skipping 308 matching lines @@
 import 'my_lib.dart';
 main() {
   for (var future in getFutures()) {
   }
 }
 ''');
     await assertHasAssistAt(
         'future in',
         DartAssistKind.ADD_TYPE_ANNOTATION,
         '''
+import 'dart:async';
 import 'my_lib.dart';
-import 'dart:async';
 main() {
   for (Future<int> future in getFutures()) {
   }
 }
 ''');
   }
 
   test_addTypeAnnotation_declaredIdentifier_OK_final() async {
     resolveTestUnit('''
 main(List<String> items) {
@@ skipping 118 matching lines @@
     resolveTestUnit('''
 import 'my_lib.dart';
 main() {
   var v = getFutureInt();
 }
 ''');
     await assertHasAssistAt(
         'v =',
         DartAssistKind.ADD_TYPE_ANNOTATION,
         '''
+import 'dart:async';
 import 'my_lib.dart';
-import 'dart:async';
 main() {
   Future<int> v = getFutureInt();
 }
 ''');
   }
 
   test_addTypeAnnotation_local_OK_addImport_notLibraryUnit() async {
     // prepare library
     addSource(
         '/my_lib.dart',
@@ skipping 27 matching lines @@
     assist = await _assertHasAssist(DartAssistKind.ADD_TYPE_ANNOTATION);
     change = assist.change;
     // verify
     {
       var testFileEdit = change.getFileEdit('/app.dart');
       var resultCode = SourceEdit.applySequence(appCode, testFileEdit.edits);
       expect(
           resultCode,
           '''
 library my_app;
+import 'dart:async';
 import 'my_lib.dart';
-import 'dart:async';
 part 'test.dart';
 ''');
     }
     {
       var testFileEdit = change.getFileEdit('/test.dart');
       var resultCode = SourceEdit.applySequence(testCode, testFileEdit.edits);
       expect(
           resultCode,
           '''
 part of my_app;
@@ skipping 19 matching lines @@
     resolveTestUnit('''
 import 'ccc/lib_b.dart';
 main() {
   var v = newMyClass();
 }
 ''');
     await assertHasAssistAt(
         'v =',
         DartAssistKind.ADD_TYPE_ANNOTATION,
         '''
+import 'aa/bbb/lib_a.dart';
 import 'ccc/lib_b.dart';
-import 'aa/bbb/lib_a.dart';
 main() {
   MyClass v = newMyClass();
 }
 ''');
   }
 
   test_addTypeAnnotation_local_OK_Function() async {
     resolveTestUnit('''
 main() {
   var v = () => 1;
@@ skipping 3378 matching lines @@
       positions.add(new Position(testFile, offset));
     }
     return positions;
   }
 
   void _setStartEndSelection() {
     offset = findOffset('// start\n') + '// start\n'.length;
     length = findOffset('// end') - offset;
   }
 }