chromeos: Introduce ash::SystemTrayTestApi

chrome/browser/chromeos/shutdown_policy_browsertest.cc

Index: chrome/browser/chromeos/shutdown_policy_browsertest.cc
diff --git a/chrome/browser/chromeos/shutdown_policy_browsertest.cc b/chrome/browser/chromeos/shutdown_policy_browsertest.cc
index 8d71ed0f194fd3573c09273bcfa840f4ad9b95d2..7a0fd698f2032fcf1768d71bcc22b2ae334e31b1 100644
--- a/chrome/browser/chromeos/shutdown_policy_browsertest.cc
+++ b/chrome/browser/chromeos/shutdown_policy_browsertest.cc
@@ -11,6 +11,7 @@
 #include "ash/system/tiles/tiles_default_view.h"
 #include "ash/system/tiles/tray_tiles.h"
 #include "ash/system/tray/system_tray.h"
+#include "ash/system/tray/system_tray_test_api.h"
 #include "base/command_line.h"
 #include "base/location.h"
 #include "base/macros.h"
@@ -157,7 +158,8 @@ class ShutdownPolicyInSessionTest
   // Gets the shutdown button view.
   const views::View* GetShutdownButton() {
     ash::SystemTray* tray = ash::Shell::Get()->GetPrimarySystemTray();
-    return tray->GetTrayTilesForTesting()
+    return ash::SystemTrayTestApi(tray)
+        .tray_tiles()
         ->GetDefaultViewForTesting()
         ->GetShutdownButtonViewForTest();
   }