Split "_Driver" tests to separate test files.

pkg/analysis_server/test/integration/analysis/update_content_driver_test.dart

+// Copyright (c) 2017, 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.
+
+import 'package:test_reflective_loader/test_reflective_loader.dart';
+
+import 'update_content_test.dart';
+
+main() {
+  defineReflectiveSuite(() {
+    defineReflectiveTests(UpdateContentTest_Driver);
+  });
+}
+
+@reflectiveTest
+class UpdateContentTest_Driver extends AbstractUpdateContentTest {
+  @override
+  bool get enableNewAnalysisDriver => true;
+}