Make cc::SurfaceId unguessable

mojo/converters/surfaces/surfaces_type_converters.cc

Index: mojo/converters/surfaces/surfaces_type_converters.cc
diff --git a/mojo/converters/surfaces/surfaces_type_converters.cc b/mojo/converters/surfaces/surfaces_type_converters.cc
index 684bdd95646ebb2cd13007266d829e3dfde92f05..af70b846acc6f71e671f4b556dfa784eda812187 100644
--- a/mojo/converters/surfaces/surfaces_type_converters.cc
+++ b/mojo/converters/surfaces/surfaces_type_converters.cc
@@ -264,10 +264,7 @@ SurfaceIdPtr TypeConverter<SurfaceIdPtr, cc::SurfaceId>::Convert(
 // static
 cc::SurfaceId TypeConverter<cc::SurfaceId, SurfaceIdPtr>::Convert(
     const SurfaceIdPtr& input) {
-  uint64_t packed_id = input->id_namespace;
-  packed_id <<= 32ull;
-  packed_id |= input->local;
-  return cc::SurfaceId(packed_id);
+  return cc::SurfaceId(input->id_namespace, input->local);
 }
 
 // static