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

ash/test/ash_test_base.cc

Index: ash/test/ash_test_base.cc
diff --git a/ash/test/ash_test_base.cc b/ash/test/ash_test_base.cc
index e1890a5a6baddfbcbd024a4637073494a67f5c19..6baece0302c6e9359b12954709a180e139f0a968 100644
--- a/ash/test/ash_test_base.cc
+++ b/ash/test/ash_test_base.cc
@@ -173,6 +173,11 @@ void AshTestBase::TearDown() {
   display::Display::SetInternalDisplayId(display::Display::kInvalidDisplayID);
 }
 
+// static
+SystemTray* AshTestBase::GetPrimarySystemTray() {
+  return Shell::GetInstance()->GetPrimarySystemTray();
+}
+
 ui::test::EventGenerator& AshTestBase::GetEventGenerator() {
   if (!event_generator_) {
     event_generator_.reset(
@@ -286,10 +291,6 @@ TestScreenshotDelegate* AshTestBase::GetScreenshotDelegate() {
   return ash_test_helper_->test_screenshot_delegate();
 }
 
-SystemTray* AshTestBase::GetPrimarySystemTray() {
-  return Shell::GetInstance()->GetPrimarySystemTray();
-}
-
 TestSystemTrayDelegate* AshTestBase::GetSystemTrayDelegate() {
   return static_cast<TestSystemTrayDelegate*>(
       WmShell::Get()->system_tray_delegate());