Clean up WindowSizer test code for ash

* Move ash-specific test helper functions into the ash unittest file
* Make all ash tests use the test harness display via UpdateDisplays()
  rather than adding an additional TestScreen
* Moved shared TestingProfile setup into test base class
* Remove unused enum Edge

Bug: 846736
Test: unit_tests
Change-Id: I062e6ec1632db5a99339c8d662d5343c963fd3f1
Reviewed-on: https://chromium-review.googlesource.com/1075723
Commit-Queue: James Cook <jamescook@chromium.org>
Reviewed-by: Michael Wasserman <msw@chromium.org>
Cr-Commit-Position: refs/heads/master@{#562501}
4 files changed