mash: Migrate ShellDelegate ownership and access to WmShell.

ash/aura/wm_shell_aura.h

Index: ash/aura/wm_shell_aura.h
diff --git a/ash/aura/wm_shell_aura.h b/ash/aura/wm_shell_aura.h
index 3c2272060b1bef3e3d3833c9b47d95e02628135f..228f39a905b894e22bfbc621d6ec78024a804ff5 100644
--- a/ash/aura/wm_shell_aura.h
+++ b/ash/aura/wm_shell_aura.h
@@ -19,7 +19,7 @@ class ASH_EXPORT WmShellAura : public WmShell,
                                public aura::client::ActivationChangeObserver,
                                public WindowTreeHostManager::Observer {
  public:
-  WmShellAura();
+  explicit WmShellAura(ShellDelegate* delegate);
   ~WmShellAura() override;
 
   static WmShellAura* Get();