Makes WindowTreeHostMus supply properties directly to window creation

ui/aura/mus/window_tree_host_mus.h

Index: ui/aura/mus/window_tree_host_mus.h
diff --git a/ui/aura/mus/window_tree_host_mus.h b/ui/aura/mus/window_tree_host_mus.h
index 40473cf39dc9ed839fa74ab6e91884b0a7b5f4ff..e29f7b0423bde2b537341b2abef873fcf3a5282f 100644
--- a/ui/aura/mus/window_tree_host_mus.h
+++ b/ui/aura/mus/window_tree_host_mus.h
@@ -30,11 +30,21 @@ class WindowTreeHostMusDelegate;
 
 class AURA_EXPORT WindowTreeHostMus : public aura::WindowTreeHostPlatform {
  public:
+  // |properties| are applied to the window created by this class (using
+  // PropertyConverter).
+  // TODO: this should take an unordered_map, see http://crbug.com/670515.
   WindowTreeHostMus(
       std::unique_ptr<WindowPortMus> window_port,
       WindowTreeClient* window_tree_client,
       int64_t display_id,
       const std::map<std::string, std::vector<uint8_t>>* properties = nullptr);
+
+  // This constructor is intended for creating top level windows in
+  // non-window-manager code. |properties| are properties passed verbatim to
+  // the server, that is, no conversion is done before sending |properties| to
+  // the server. Additionally |properties| are passed to PropertyConverter and
+  // any known properties are set on the Window created by this class.
+  // TODO: this should take an unordered_map, see http://crbug.com/670515.
   explicit WindowTreeHostMus(
       WindowTreeClient* window_tree_client,
       const std::map<std::string, std::vector<uint8_t>>* properties = nullptr);