Use mojo SystemTray interfaces for both mash and classic ash

ash/aura/wm_shell_aura.cc

Index: ash/aura/wm_shell_aura.cc
diff --git a/ash/aura/wm_shell_aura.cc b/ash/aura/wm_shell_aura.cc
index 9d112c51d3804fe69d0474526f653344a57d4e9b..a34cc4c6b2d343b425b5b703cad5d86a1120f9fe 100644
--- a/ash/aura/wm_shell_aura.cc
+++ b/ash/aura/wm_shell_aura.cc
@@ -77,6 +77,10 @@ void WmShellAura::Shutdown() {
   WmShell::Shutdown();
 }
 
+bool WmShellAura::IsRunningInMash() const {
+  return false;
+}
+
 WmWindow* WmShellAura::NewWindow(ui::wm::WindowType window_type,
                                  ui::LayerType layer_type) {
   aura::Window* aura_window = new aura::Window(nullptr);