Add ChromeOS file manager integration test.

Adds a test equivalent to the ChromeOS Tast test
filemanager.LaunchFromShelfContextMenu. This verifies that
right-clicking on the file manager shelf item and selecting "new window"
opens the File Manager.

Some new helpers are added to //ui/aura/test to do some window
finding operations that are common in ChromeOS Tast tests.

Add a helper function to InteractiveAshTest to block until a
window with a given title exists (also common in Tast tests but
not possible to add to //ui/aura/test).

Element identifiers were added to the app services' menus to
facilitate testing with Kombucha.

Change-Id: I61ed973281a5743592b74267cac53bba03f2e727
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4739780
Reviewed-by: Dominick Ng <dominickn@chromium.org>
Reviewed-by: James Cook <jamescook@chromium.org>
Commit-Queue: Brett Wilson <brettw@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1189645}

diff --git a/ui/aura/BUILD.gn b/ui/aura/BUILD.gn
index fdd7c76..50ca856 100644
--- a/ui/aura/BUILD.gn
+++ b/ui/aura/BUILD.gn

@@ -192,6 +192,7 @@
     "test/env_test_helper.h",
     "test/event_generator_delegate_aura.cc",
     "test/event_generator_delegate_aura.h",
+    "test/find_window.h",
     "test/test_cursor_client.cc",
     "test/test_cursor_client.h",
     "test/test_focus_client.cc",