[mojo-edk] Add MojoWatch and MojoCancelWatch APIs

mojo/edk/system/dispatcher.cc

Index: mojo/edk/system/dispatcher.cc
diff --git a/mojo/edk/system/dispatcher.cc b/mojo/edk/system/dispatcher.cc
index 8a2e15e959c3ed9e344f2c4700a301ae1dcec2ee..6705542ecf75ca67cb273506f349f5daaa021cc4 100644
--- a/mojo/edk/system/dispatcher.cc
+++ b/mojo/edk/system/dispatcher.cc
@@ -22,6 +22,16 @@ Dispatcher::DispatcherInTransit::DispatcherInTransit(
 
 Dispatcher::DispatcherInTransit::~DispatcherInTransit() {}
 
+MojoResult Dispatcher::Watch(MojoHandleSignals signals,
+                             const Watcher::WatchCallback& callback,
+                             uintptr_t context) {
+  return MOJO_RESULT_INVALID_ARGUMENT;
+}
+
+MojoResult Dispatcher::CancelWatch(uintptr_t context) {
+  return MOJO_RESULT_INVALID_ARGUMENT;
+}
+
 MojoResult Dispatcher::WriteMessage(const void* bytes,
                                     uint32_t num_bytes,
                                     const DispatcherInTransit* dispatchers,