mash: remove more shell/shelf WmWindow usage.

ash/mus/bridge/shell_port_mash.cc

Index: ash/mus/bridge/shell_port_mash.cc
diff --git a/ash/mus/bridge/shell_port_mash.cc b/ash/mus/bridge/shell_port_mash.cc
index 9b922f34c8b1e3e36567c9102e3469c6988c1880..9269004be3de226df1ab170864af4159f01744a5 100644
--- a/ash/mus/bridge/shell_port_mash.cc
+++ b/ash/mus/bridge/shell_port_mash.cc
@@ -113,7 +113,7 @@ ShellPortMash::MusSpecificState::MusSpecificState() = default;
 ShellPortMash::MusSpecificState::~MusSpecificState() = default;
 
 ShellPortMash::ShellPortMash(
-    WmWindow* primary_root_window,
+    aura::Window* primary_root_window,
     WindowManager* window_manager,
     views::PointerWatcherEventRouter* pointer_watcher_event_router,
     bool create_session_state_delegate_stub)
@@ -179,11 +179,9 @@ Config ShellPortMash::GetAshConfig() const {
   return window_manager_->config();
 }
 
-WmWindow* ShellPortMash::GetPrimaryRootWindow() {
-  if (GetAshConfig() == Config::MUS) {
-    return WmWindow::Get(
-        Shell::Get()->window_tree_host_manager()->GetPrimaryRootWindow());
-  }
+aura::Window* ShellPortMash::GetPrimaryRootWindow() {
+  if (GetAshConfig() == Config::MUS)
+    return Shell::Get()->window_tree_host_manager()->GetPrimaryRootWindow();
   // NOTE: This is called before the RootWindowController has been created, so
   // it can't call through to RootWindowController to get all windows.
   return primary_root_window_;