mash: Fix MusPropertyMirrorAsh for owned properties; add test.

ash/public/cpp/BUILD.gn

Index: ash/public/cpp/BUILD.gn
diff --git a/ash/public/cpp/BUILD.gn b/ash/public/cpp/BUILD.gn
index 521d9fbbf9f4e573ef7436e006380ae1cc7d8099..6251a02c2b05a97d670c698c272beccf46b85212 100644
--- a/ash/public/cpp/BUILD.gn
+++ b/ash/public/cpp/BUILD.gn
@@ -5,13 +5,21 @@
 # C++ headers and sources that can be used outside ash.
 source_set("cpp") {
   sources = [
+    "mus_property_mirror_ash.cc",
+    "mus_property_mirror_ash.h",
     "session_types.h",
+    "shelf_item_types.cc",
+    "shelf_item_types.h",
     "shelf_types.h",
     "shell_window_ids.cc",
     "shell_window_ids.h",
+    "window_properties.cc",
+    "window_properties.h",
   ]
 
   deps = [
     "//base",
+    "//ui/aura",
+    "//ui/views/mus",
   ]
 }