Print Preview: Refactor some tests

- Move pages and scaling tests into the test files for these tests
- Simplify pages test, to only validate changing the dropdown, since
  the rest of this test is duplicating other tests.
- Add and modify utility methods for setting dropdowns/inputs and
  use in pages/scaling tests and elsewhere
- Split pages tests into interactive_ui_tests and browser_tests more
  clearly, and remove duplicates.

Change-Id: I6a1cce70d5b222f843badfbe8a8508ebcb309b16
Reviewed-on: https://chromium-review.googlesource.com/c/1487147
Commit-Queue: Rebekah Potter <rbpotter@chromium.org>
Reviewed-by: Esmael El-Moslimany <aee@chromium.org>
Cr-Commit-Position: refs/heads/master@{#636032}
7 files changed