mash: Migrate ShellDelegate ownership and access to WmShell.

ash/mus/bridge/wm_shell_mus.h

Index: ash/mus/bridge/wm_shell_mus.h
diff --git a/ash/mus/bridge/wm_shell_mus.h b/ash/mus/bridge/wm_shell_mus.h
index 17ad9fbcc218e80a511de4c315df218599b17897..4ad4d413f9e40447991a2e4c1782e21e9acfe8af 100644
--- a/ash/mus/bridge/wm_shell_mus.h
+++ b/ash/mus/bridge/wm_shell_mus.h
@@ -27,7 +27,7 @@ class WmWindowMus;
 // WmShell implementation for mus.
 class WmShellMus : public WmShell, public ::ui::WindowTreeClientObserver {
  public:
-  explicit WmShellMus(::ui::WindowTreeClient* client);
+  WmShellMus(ShellDelegate* delegate, ::ui::WindowTreeClient* client);
   ~WmShellMus() override;
 
   static WmShellMus* Get();