Add Core methods for wait set.

mojo/edk/system/wait_set_dispatcher.h

Index: mojo/edk/system/wait_set_dispatcher.h
diff --git a/mojo/edk/system/wait_set_dispatcher.h b/mojo/edk/system/wait_set_dispatcher.h
index 6c6d6c91a454d10874c6e21e9b5810f75024fcd8..6dc5c71d89dd4c29053ee0421b0fcce20cc9fb3c 100644
--- a/mojo/edk/system/wait_set_dispatcher.h
+++ b/mojo/edk/system/wait_set_dispatcher.h
@@ -108,10 +108,11 @@ class WaitSetDispatcher final : public Dispatcher, public Awakable {
   util::RefPtr<Dispatcher> CreateEquivalentDispatcherAndCloseImplNoLock(
       MessagePipe* message_pipe,
       unsigned port) override;
-  MojoResult WaitSetAddImpl(UserPointer<const MojoWaitSetAddOptions> options,
-                            util::RefPtr<Dispatcher>&& dispatcher,
-                            MojoHandleSignals signals,
-                            uint64_t cookie) override;
+  MojoResult WaitSetAddImpl(
+      util::RefPtr<Dispatcher>&& dispatcher,
+      MojoHandleSignals signals,
+      uint64_t cookie,
+      UserPointer<const MojoWaitSetAddOptions> options) override;
   MojoResult WaitSetRemoveImpl(uint64_t cookie) override;
   MojoResult WaitSetWaitImpl(MojoDeadline deadline,
                              UserPointer<uint32_t> num_results,