Change mojo geometry structs from using type converters to StructTraits.

ui/mojo/typemaps.gni

Index: ui/mojo/typemaps.gni
diff --git a/ui/base/ui_features.gni b/ui/mojo/typemaps.gni
similarity index 75%
copy from ui/base/ui_features.gni
copy to ui/mojo/typemaps.gni
index 724c4d4496852f1e480b97542f86ea35dc4a162e..fafb20f220da1750ec9855f63d02712f52ccc689 100644
--- a/ui/base/ui_features.gni
+++ b/ui/mojo/typemaps.gni
@@ -2,4 +2,4 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-enable_hidpi = is_mac || is_win || is_linux
+typemaps = [ "//ui/mojo/geometry/geometry.typemap" ]