mash: Port TrayUpdateTest to AshTest

ash/common/test/ash_test.h

Index: ash/common/test/ash_test.h
diff --git a/ash/common/test/ash_test.h b/ash/common/test/ash_test.h
index ef1901d5d013c0850aa9757fa4107e0902030d37..886161a33a2799bc1de87234c6e1d9782e2f497d 100644
--- a/ash/common/test/ash_test.h
+++ b/ash/common/test/ash_test.h
@@ -27,6 +27,7 @@ class WidgetDelegate;
 namespace ash {
 
 class AshTestImpl;
+class SystemTray;
 class WmShelf;
 class WmWindow;
 
@@ -63,6 +64,9 @@ class AshTest : public testing::Test {
   // Returns the WmShelf for the primary display.
   static WmShelf* GetPrimaryShelf();
 
+  // Returns the system tray on the primary display.
+  static SystemTray* GetPrimarySystemTray();
+
   bool SupportsMultipleDisplays() const;
 
   // Update the display configuration as given in |display_spec|.