Add a mojom/StructTrait for display::Display.

ui/display/display.h

Index: ui/display/display.h
diff --git a/ui/display/display.h b/ui/display/display.h
index 72f8b8cb5a73dcf721bfe7fd0f6b37f47cf7d931..c3ae3092e519d3c7ddd24e931547612bd5a2bceb 100644
--- a/ui/display/display.h
+++ b/ui/display/display.h
@@ -11,8 +11,18 @@
 #include "ui/display/display_export.h"
 #include "ui/gfx/geometry/rect.h"
 
+#if !defined(OS_IOS)
+#include "mojo/public/cpp/bindings/struct_traits.h"  // nogncheck
+#endif
+
 namespace display {
 
+#if !defined(OS_IOS)
+namespace mojom {
+class Display;
+}
+#endif
+
 // This class typically, but does not always, correspond to a physical display
 // connected to the system. A fake Display may exist on a headless system, or a
 // Display may correspond to a remote, virtual display.
@@ -162,6 +172,10 @@ class DISPLAY_EXPORT Display final {
   Rotation rotation_;
   TouchSupport touch_support_;
   gfx::Size maximum_cursor_size_;
+
+#if !defined(OS_IOS)
+  friend struct mojo::StructTraits<display::mojom::Display, display::Display>;
+#endif
 };
 
 }  // namespace display