Extract testing utilities into a separate package.

pkg/analyzer/test/index/store/collection_test.dart

Index: pkg/analyzer/test/index/store/collection_test.dart
diff --git a/pkg/analyzer/test/index/store/collection_test.dart b/pkg/analyzer/test/index/store/collection_test.dart
index c384515d801c9f29f6f7ff1087a0090f99efb15f..636b0a3151b7d22c06957fba576e47a44dc8d5e3 100644
--- a/pkg/analyzer/test/index/store/collection_test.dart
+++ b/pkg/analyzer/test/index/store/collection_test.dart
@@ -4,11 +4,10 @@
 
 library test.engine.src.index.store.collection;
 
+import 'package:analysis_testing/reflective_tests.dart';
 import 'package:analyzer/src/index/store/collection.dart';
 import 'package:unittest/unittest.dart';
 
-import '../../reflective_tests.dart';
-
 
 main() {
   groupSep = ' | ';