mash: Migrate wallpaper controllers to ash/common.

ash/mus/window_manager.h

Index: ash/mus/window_manager.h
diff --git a/ash/mus/window_manager.h b/ash/mus/window_manager.h
index 89b4a96b514fa020a541bf92a955072311c8efe1..8d6ff15c88c043381daa2c241b06037002c5a762 100644
--- a/ash/mus/window_manager.h
+++ b/ash/mus/window_manager.h
@@ -11,6 +11,7 @@
 #include <set>
 
 #include "base/macros.h"
+#include "base/memory/ref_counted.h"
 #include "base/observer_list.h"
 #include "services/ui/common/types.h"
 #include "services/ui/public/cpp/window_manager_delegate.h"
@@ -18,6 +19,10 @@
 #include "services/ui/public/cpp/window_tree_client_delegate.h"
 #include "services/ui/public/interfaces/window_manager.mojom.h"
 
+namespace base {
+class SequencedWorkerPool;
+}
+
 namespace display {
 class Display;
 class ScreenBase;
@@ -53,7 +58,8 @@ class WindowManager : public ui::WindowManagerDelegate,
   explicit WindowManager(shell::Connector* connector);
   ~WindowManager() override;
 
-  void Init(std::unique_ptr<ui::WindowTreeClient> window_tree_client);
+  void Init(std::unique_ptr<ui::WindowTreeClient> window_tree_client,
+            const scoped_refptr<base::SequencedWorkerPool>& blocking_pool);
 
   WmShellMus* shell() { return shell_.get(); }