Enable and update app_management_view/main_view_test.js

main_view_test was disabled and out of date with the latest
iteration of main_view_test. One out of date test is removed
and another is updated to reflect recent changes.

This is done to prepare for Polymer 3 migration.

Bug: 1045266
Change-Id: Ic5855d0df4ce50aef6c48f613fce20b342723229
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2653659
Commit-Queue: Claude van der Merwe <cvandermerwe@google.com>
Reviewed-by: Jeevan Shikaram <jshikaram@chromium.org>
Reviewed-by: Kyle Horimoto <khorimoto@chromium.org>
Cr-Commit-Position: refs/heads/master@{#850266}