Restructure outline shaker tests.

pkg/front_end/testcases/shaker/lib/sources.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.
+
+class A1 {}
+
+class A2 {}
+
+class A3 {}
+
+class A4 {}
+
+class A5 {}
+
+class A6 {}
+
+class A7 {}
+
+class A8 {}
+
+class A9 {}
+
+class A10 {}
+
+class A11 {}
+
+class A12 {}
+
+class A13 {}
+
+class A14 {}
+
+class A15 {}