Enable app_list integration tests on linux_aura, and class some as interactive_ui_tests.

The app list uses focus to make itself disappear, so tests are currently
failing flakily when a concurrent browser test is stealing focus away.

This CL moves the app list browser tests that depend on querying the app
list visibility to interactive_ui_tests, stands them up on linux_aura,
and re-enables ShowAppListBrowserTest.ShowAppListFlag (as
ShowAppListInteractiveTest) which was disabled for being flaky.

Making the tests interactive_ui_tests runs them in serial, which
prevents the focus being stolen away from the app launcher, which would
cause the window to be dismissed before the test had completed.

BUG=315677, 299250

Review URL: https://codereview.chromium.org/107343005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@241563 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 241563