chromeos: Introduce ash::SystemTrayTestApi

chrome/browser/ui/ash/system_tray_tray_cast_browsertest_media_router_chromeos.cc

Index: chrome/browser/ui/ash/system_tray_tray_cast_browsertest_media_router_chromeos.cc
diff --git a/chrome/browser/ui/ash/system_tray_tray_cast_browsertest_media_router_chromeos.cc b/chrome/browser/ui/ash/system_tray_tray_cast_browsertest_media_router_chromeos.cc
index 79ecb4deb2a1dfd4eeef678e96c8bf139661ea5d..f7370c91b1938c3114895304ba013bacaf491186 100644
--- a/chrome/browser/ui/ash/system_tray_tray_cast_browsertest_media_router_chromeos.cc
+++ b/chrome/browser/ui/ash/system_tray_tray_cast_browsertest_media_router_chromeos.cc
@@ -7,6 +7,7 @@
 #include "ash/shell.h"
 #include "ash/system/tray/system_tray.h"
 #include "ash/system/tray/system_tray_delegate.h"
+#include "ash/system/tray/system_tray_test_api.h"
 #include "ash/test/tray_cast_test_api.h"
 #include "base/macros.h"
 #include "chrome/browser/media/router/media_routes_observer.h"
@@ -46,7 +47,7 @@ ash::TrayCast* GetTrayCast() {
   // not be created.
   tray->ShowDefaultView(ash::BubbleCreationType::BUBBLE_CREATE_NEW);
 
-  return tray->GetTrayCastForTesting();
+  return ash::SystemTrayTestApi(tray).tray_cast();
 }
 
 class SystemTrayTrayCastMediaRouterChromeOSTest : public InProcessBrowserTest {