Change mojo geometry structs from using type converters to StructTraits.

ash/mus/keyboard_ui_mus.cc

Index: ash/mus/keyboard_ui_mus.cc
diff --git a/ash/mus/keyboard_ui_mus.cc b/ash/mus/keyboard_ui_mus.cc
index d2ca388071fc2d19d8188acbdaee46086080ce43..61633764e10e4d626728dd70d7d5bf0d6938e0e6 100644
--- a/ash/mus/keyboard_ui_mus.cc
+++ b/ash/mus/keyboard_ui_mus.cc
@@ -42,7 +42,7 @@ bool KeyboardUIMus::IsEnabled() {
 void KeyboardUIMus::OnKeyboardStateChanged(bool is_enabled,
                                            bool is_visible,
                                            uint64_t display_id,
-                                           mojo::RectPtr bounds) {
+                                           const gfx::Rect& bounds) {
   if (is_enabled_ == is_enabled)
     return;