Bug 1505223 - Add mozilla::Tuple to ServoBindings.toml r=emilio

Differential Revision: https://phabricator.services.mozilla.com/D11134

--HG--
extra : moz-landing-system : lando

layout/style/ServoBindings.toml

@@ -354,6 +354,7 @@ opaque-types = [
     "mozilla::Pair_Base",
     "mozilla::SeenPtrs",
     "mozilla::SupportsWeakPtr",
+    "mozilla::Tuple",
     "SupportsWeakPtr",
     "mozilla::detail::WeakReference",
     "mozilla::WeakPtr",