Bug 1441308 - Support moving Maybe's in IPC serialization r=mccr8

I'd like to move an ipc::ByteBuf member of a struct into a Maybe,
and in order for that to work IPDLParamTraits<Maybe> needs to support
the rvalue Write.

Differential Revision: https://phabricator.services.mozilla.com/D23986

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

ipc/glue/IPDLParamTraits.h

@@ -189,6 +189,16 @@ struct IPDLParamTraits<mozilla::Maybe<T>> {
     }
   }
 
+  static void Write(IPC::Message* aMsg, IProtocol* aActor,
+                    mozilla::Maybe<T>&& aParam) {
+    bool isSome = aParam.isSome();
+    WriteIPDLParam(aMsg, aActor, isSome);
+
+    if (isSome) {
+      WriteIPDLParam(aMsg, aActor, std::move(aParam.ref()));
+    }
+  }
+
   static bool Read(const IPC::Message* aMsg, PickleIterator* aIter,
                    IProtocol* aActor, mozilla::Maybe<T>* aResult) {
     bool isSome;