Unified: Hide UnifiedSystemTray in kiosk app mode.

On Kiosk mode, we shouldn't show volume slider bubble. The check was
missing in UnifiedSystemTray. It caused UI regression in Kiosk devices.
(See the bug for detail).

TEST=manual(confirmed on a Kiosk device that the slider is not shown)
BUG=888890

Change-Id: I00359892b6bfc624b95c5f2a57fc7802b38a4dca
Reviewed-on: https://chromium-review.googlesource.com/1247841Reviewed-by: Yoshiki Iguchi <yoshiki@chromium.org>
Commit-Queue: Tetsui Ohkubo <tetsui@chromium.org>
Cr-Commit-Position: refs/heads/master@{#594609}

ash/system/unified/unified_slider_bubble_controller.cc

@@ -6,6 +6,7 @@
 
 #include "ash/public/cpp/app_list/app_list_features.h"
 #include "ash/root_window_controller.h"
+#include "ash/session/session_controller.h"
 #include "ash/shell.h"
 #include "ash/system/brightness/unified_brightness_slider_controller.h"
 #include "ash/system/keyboard_brightness/unified_keyboard_brightness_slider_controller.h"
@@ -113,6 +114,10 @@ void UnifiedSliderBubbleController::OnAudioSettingsButtonClicked() {
 }
 
 void UnifiedSliderBubbleController::ShowBubble(SliderType slider_type) {
+  // Never show slider bubble in kiosk app mode.
+  if (Shell::Get()->session_controller()->IsRunningInAppMode())
+    return;
+
   if (IsAnyMainBubbleShown()) {
     tray_->EnsureBubbleExpanded();
     return;

ash/system/unified/unified_system_tray.cc

@@ -311,6 +311,10 @@ void UnifiedSystemTray::UpdateAfterShelfAlignmentChange() {
 }
 
 void UnifiedSystemTray::ShowBubbleInternal(bool show_by_click) {
+  // Never show System Tray bubble in kiosk app mode.
+  if (Shell::Get()->session_controller()->IsRunningInAppMode())
+    return;
+
   // Hide volume/brightness slider popup.
   slider_bubble_controller_->CloseBubble();