mash: Migrate wallpaper controllers to ash/common.

ash/mus/test/wm_test_helper.h

Index: ash/mus/test/wm_test_helper.h
diff --git a/ash/mus/test/wm_test_helper.h b/ash/mus/test/wm_test_helper.h
index 3e125a2ee6f78f0f9ff695b9ea47e7ac13d8b329..cc444c7a5a9740a4324653fe72c546311443ba2c 100644
--- a/ash/mus/test/wm_test_helper.h
+++ b/ash/mus/test/wm_test_helper.h
@@ -9,6 +9,7 @@
 
 #include "ash/mus/window_manager_application.h"
 #include "base/macros.h"
+#include "base/test/sequenced_worker_pool_owner.h"

[James Cook, 2016/09/08 20:27:55]

nit: maybe for a followup CL, can this be forward declared?

[msw, 2016/09/08 20:41:40]

Done.

 #include "services/ui/public/cpp/tests/test_window_tree_client_setup.h"
 
 namespace base {
@@ -48,6 +49,7 @@ class WmTestHelper {
   ui::TestWindowTreeClientSetup window_tree_client_setup_;
   std::unique_ptr<WindowManagerApplication> window_manager_app_;
   WmTestScreen* screen_ = nullptr;  // Owned by |window_manager_app_|.
+  std::unique_ptr<base::SequencedWorkerPoolOwner> blocking_pool_owner_;
 
   DISALLOW_COPY_AND_ASSIGN(WmTestHelper);
 };