mash: Move TrayUpdate to //ash/common

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 6ce049e4804e993eda7ea2e28f7e9f398e434a12..ab9be2969fecd72e1e5ac22beb0a46999f25b260 100644
--- a/ash/test/ash_test_base.cc
+++ b/ash/test/ash_test_base.cc
@@ -272,6 +272,10 @@ 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());