Close system tray when no further user interaction is expected on it.

Close the system tray bubble when these actions are taken.
- Switch to another user
- Sign in another user
- Lock screen

Bug: 859041
Test: verified manually
Change-Id: Id70d71e73a5c261212bbbb13d52f376275da8002
Reviewed-on: https://chromium-review.googlesource.com/1127914Reviewed-by: Tetsui Ohkubo <tetsui@chromium.org>
Reviewed-by: Yoshiki Iguchi <yoshiki@chromium.org>
Commit-Queue: Tatsuhisa Yamaguchi <yamaguchi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#574077}

ash/system/unified/unified_system_tray_controller.cc

@@ -103,11 +103,13 @@ void UnifiedSystemTrayController::HandleUserSwitch(int user_index) {
       MultiProfileUMA::SWITCH_ACTIVE_USER_BY_TRAY);
   controller->SwitchActiveUser(
       controller->GetUserSession(user_index)->user_info->account_id);
+  CloseBubble();
 }
 
 void UnifiedSystemTrayController::HandleAddUserAction() {
   MultiProfileUMA::RecordSigninUser(MultiProfileUMA::SIGNIN_USER_BY_TRAY);
   Shell::Get()->session_controller()->ShowMultiProfileLogin();
+  CloseBubble();
 }
 
 void UnifiedSystemTrayController::HandleSignOutAction() {
@@ -120,6 +122,7 @@ void UnifiedSystemTrayController::HandleLockAction() {
   chromeos::DBusThreadManager::Get()
       ->GetSessionManagerClient()
       ->RequestLockScreen();
+  CloseBubble();
 }
 
 void UnifiedSystemTrayController::HandleSettingsAction() {