Remove DisplayStructTraitsTest interface.

ui/display/mojo/display_snapshot_mojo_struct_traits.cc

Index: ui/display/mojo/display_snapshot_mojo_struct_traits.cc
diff --git a/ui/display/mojo/display_snapshot_mojo_struct_traits.cc b/ui/display/mojo/display_snapshot_mojo_struct_traits.cc
index 0a490e5e26d474cdc018a9483d268c668e040db5..1a370dc87ab5869fcdef2f508fae681f62a4590e 100644
--- a/ui/display/mojo/display_snapshot_mojo_struct_traits.cc
+++ b/ui/display/mojo/display_snapshot_mojo_struct_traits.cc
@@ -4,11 +4,7 @@
 
 #include "ui/display/mojo/display_snapshot_mojo_struct_traits.h"
 
-#include "ipc/ipc_message_utils.h"
-#include "ui/display/mojo/display_constants_struct_traits.h"
-#include "ui/display/mojo/display_mode_struct_traits.h"
 #include "ui/display/types/display_constants.h"
-#include "ui/gfx/geometry/mojo/geometry_struct_traits.h"
 #include "ui/gfx/geometry/size.h"
 
 namespace mojo {
@@ -136,4 +132,4 @@ bool StructTraits<display::mojom::DisplaySnapshotMojoDataView,
   return true;
 }
 
-}  // namespace mojo
+}  // namespace mojo