rename completion source files to match content

pkg/analysis_server/test/services/completion/prefixed_element_contributor_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.completion.invocation;
 
 import 'dart:async';
 
 import 'package:analysis_server/src/protocol.dart';
 import 'package:analysis_server/src/services/completion/dart_completion_manager.dart';
-import 'package:analysis_server/src/services/completion/invocation_computer.dart';
+import 'package:analysis_server/src/services/completion/prefixed_element_contributor.dart';
 import 'package:unittest/unittest.dart';
 
 import '../../reflective_tests.dart';
 import 'completion_test_util.dart';
 
 main() {
   groupSep = ' | ';
   runReflectiveTests(PrefixedElementContributorTest);
 }
 
@@ skipping 485 matching lines @@
 }
 void test(Derived d) {
   d.^
 }
 ''');
     return computeFull((bool result) {
       assertSuggestMethod('f', 'Base', 'void');
     });
   }
 }