Rework contribution sorter to use futures

pkg/analysis_server/test/services/completion/test_all.dart

Index: pkg/analysis_server/test/services/completion/test_all.dart
diff --git a/pkg/analysis_server/test/services/completion/test_all.dart b/pkg/analysis_server/test/services/completion/test_all.dart
index dba0885e4116578e9c2ff98a7b9805a88cd6e791..f4129eed0c0190f2f3f9f12395c0e5dfb0672635 100644
--- a/pkg/analysis_server/test/services/completion/test_all.dart
+++ b/pkg/analysis_server/test/services/completion/test_all.dart
@@ -9,7 +9,6 @@ import 'package:unittest/unittest.dart';
 import '../../utils.dart';
 import 'arglist_contributor_test.dart' as arglist_test;
 import 'combinator_contributor_test.dart' as combinator_test;
-import 'common_usage_computer_test.dart' as common_usage_computer_test;
 import 'completion_computer_test.dart' as completion_computer_test;
 import 'completion_manager_test.dart' as completion_manager_test;
 import 'completion_target_test.dart' as completion_target_test;
@@ -29,7 +28,6 @@ main() {
   group('completion', () {
     arglist_test.main();
     combinator_test.main();
-    common_usage_computer_test.main();
     completion_computer_test.main();
     completion_manager_test.main();
     completion_target_test.main();