mash: Break ash system tray dependencies on ash::ShelfWidget

ash/test/ash_test_base.h

Index: ash/test/ash_test_base.h
diff --git a/ash/test/ash_test_base.h b/ash/test/ash_test_base.h
index df73c7d848f1a5e3d357d9af3a9fe4e882f2db51..8a7bd7ccf04827324aef1a0134e49dd952dc83f5 100644
--- a/ash/test/ash_test_base.h
+++ b/ash/test/ash_test_base.h
@@ -63,6 +63,9 @@ class AshTestBase : public testing::Test {
   void SetUp() override;
   void TearDown() override;
 
+  // Returns the system tray on the primary display.
+  static SystemTray* GetPrimarySystemTray();
+
   // Update the display configuration as given in |display_specs|.
   // See ash::test::DisplayManagerTestApi::UpdateDisplay for more details.
   void UpdateDisplay(const std::string& display_specs);
@@ -129,9 +132,6 @@ class AshTestBase : public testing::Test {
 
   TestScreenshotDelegate* GetScreenshotDelegate();
 
-  // Returns the system tray on the primary display.
-  SystemTray* GetPrimarySystemTray();
-
   TestSystemTrayDelegate* GetSystemTrayDelegate();
 
   // Utility methods to emulate user logged in or not, session started or not