Refactor an Application unittest fixture.

[chhamilton]

A common pattern in testing applications is to build a harness that captures their various outputs and makes them available for parsing by the fixture. This pattern occurs 25 times in the code base via cut and paste. It would be great to extract a reusable fixture:

https://codereview.chromium.org/1269553002/diff/1/syzygy/runlaa/runlaa_app_unittest.cc#newcode51