Remove an ash reference from the user adding screen.

      system tray still works

Bug: 327885
Test: sign into one user, start signin to a second user, cancel;
Change-Id: I9fa93bbd87a1f4a0087746e3a42ead07ee308710
Reviewed-on: https://chromium-review.googlesource.com/1008825
Commit-Queue: Evan Stade <estade@chromium.org>
Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#551120}

chrome/browser/chromeos/login/ui/user_adding_screen.cc

@@ -4,8 +4,6 @@
 
 #include "chrome/browser/chromeos/login/ui/user_adding_screen.h"
 
-#include "ash/shell.h"
-#include "ash/system/tray/system_tray.h"
 #include "base/bind.h"
 #include "base/memory/singleton.h"
 #include "base/observer_list.h"
@@ -62,8 +60,6 @@ void UserAddingScreenImpl::Start() {
 void UserAddingScreenImpl::Cancel() {
   CHECK(IsRunning());
 
-  // Make sure that system tray is enabled after this flow.
-  ash::Shell::Get()->GetPrimarySystemTray()->SetEnabled(true);
   display_host_->CancelUserAdding();
 
   // Reset wallpaper if cancel adding user from multiple user sign in page.

testing/buildbot/filters/mash.browser_tests.filter

@@ -247,9 +247,6 @@
 # ash::Shell access in test.
 -TrayAccessibilityTestInstance/TrayAccessibilityTest.*
 
-# chromeos::UserAddingScreenImpl::Cancel() uses ash::Shell to enable system tray.
--UserAddingScreenTest.*
-
 # Virtual keyboard not supported.
 -AccessibilityManagerLoginTest.ResumeSavedPref
 -DefaultKeyboardExtensionBrowserTest.*