mustash: Convert TraySupervisedUserTest 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 886161a33a2799bc1de87234c6e1d9782e2f497d..b79c7e01414ab28dc30352f096fd7db62f22250a 100644
--- a/ash/common/test/ash_test.h
+++ b/ash/common/test/ash_test.h
@@ -31,6 +31,10 @@ class SystemTray;
 class WmShelf;
 class WmWindow;
 
+namespace test {
+class TestSystemTrayDelegate;
+}
+
 // Wraps a WmWindow calling WmWindow::Destroy() from the destructor. WmWindow is
 // owned by the corresponding window implementation. The only way to delete
 // WmWindow is to call WmWindow::Destroy(), which deletes the corresponding
@@ -67,6 +71,8 @@ class AshTest : public testing::Test {
   // Returns the system tray on the primary display.
   static SystemTray* GetPrimarySystemTray();
 
+  static test::TestSystemTrayDelegate* GetSystemTrayDelegate();
+
   bool SupportsMultipleDisplays() const;
 
   // Update the display configuration as given in |display_spec|.