Port some a11y tests from browser to ash

This CL ports following tests from browser to ash:
* TrayAccessibilityTest.ClickDetailMenu
* TrayAccessibilityTest.CheckMarksOnDetailMenu

Other TrayAccessibilityTest browser_tests will be refactored to use
SystemTrayTestApi mojo interface and kept on the browser side, because
these tests are hard to do in ash unit tests.

This CL also removes following tests:
* TrayAccessibilityTest.ShowTrayIcon (browser_tests)
* TrayAccessibilityTest.VisibilityFromMenu (ash_unittests)
* TrayAccessibilityTest.VisibilityFromSettings (ash_unittests)
* TrayAccessibilityLoginScreenTest.LoginStatus (ash_unittests)
They either have the replacement in
AccessibilityFeaturePodControllerTest, or simply the feature is removed.

TEST=ash_unittests, browser_tests
BUG=850014

Change-Id: I4d7c8d99cb6ce5df9de4115d874fc56d7a0c276a
Reviewed-on: https://chromium-review.googlesource.com/c/1306937
Commit-Queue: Tetsui Ohkubo <tetsui@chromium.org>
Reviewed-by: James Cook <jamescook@chromium.org>
Cr-Commit-Position: refs/heads/master@{#604119}

ash/system/unified/unified_detailed_view_delegate.h

@@ -5,6 +5,7 @@
 #ifndef ASH_SYSTEM_UNIFIED_UNIFIED_DETAILED_VIEW_DELEGATE_H_
 #define ASH_SYSTEM_UNIFIED_UNIFIED_DETAILED_VIEW_DELEGATE_H_
 
+#include "ash/ash_export.h"
 #include "ash/system/tray/detailed_view_delegate.h"
 #include "base/macros.h"
 
@@ -13,7 +14,7 @@ namespace ash {
 class UnifiedSystemTrayController;
 
 // Default implementation of DetailedViewDelegate for UnifiedSystemTray.
-class UnifiedDetailedViewDelegate : public DetailedViewDelegate {
+class ASH_EXPORT UnifiedDetailedViewDelegate : public DetailedViewDelegate {
  public:
   explicit UnifiedDetailedViewDelegate(
       UnifiedSystemTrayController* tray_controller);