Add Unit Test for WindowDataLayer

This PR provides a unit test for WindowDataLayer.

The purpose of this unit test is to protect against issues while the data layer design is improved (such as #1089 and #1125).
@jeffdonahue Yes, it is intentional. The `sample_window.txt` is used for make while `sample_window.txt.in` is used for cmake. It is similar to `sample_data_list.txt` and `sample_data_list.txt.in` used for HDF5 test.