Change mojo geometry structs from using type converters to StructTraits.

ash/mus/keyboard_ui_mus.h

Index: ash/mus/keyboard_ui_mus.h
diff --git a/ash/mus/keyboard_ui_mus.h b/ash/mus/keyboard_ui_mus.h
index 6e12585113bc582beb36602620ecc26172088da6..7ef4d45c11366511f1025e5b78c0a9ff0dc03b48 100644
--- a/ash/mus/keyboard_ui_mus.h
+++ b/ash/mus/keyboard_ui_mus.h
@@ -35,7 +35,7 @@ class KeyboardUIMus : public KeyboardUI,
   void OnKeyboardStateChanged(bool is_enabled,
                               bool is_visible,
                               uint64_t display_id,
-                              mojo::RectPtr bounds) override;
+                              const gfx::Rect& bounds) override;
 
  private:
   bool is_enabled_;