[mojo-edk] Add MojoWatch and MojoCancelWatch APIs

mojo/edk/system/dispatcher.h

Index: mojo/edk/system/dispatcher.h
diff --git a/mojo/edk/system/dispatcher.h b/mojo/edk/system/dispatcher.h
index 8bdff2834cf0ffca91d1372d57311e8730140aee..0ae45826b7bd49dc206a987015f47d15e9ce1fc8 100644
--- a/mojo/edk/system/dispatcher.h
+++ b/mojo/edk/system/dispatcher.h
@@ -20,6 +20,7 @@
 #include "mojo/edk/system/handle_signals_state.h"
 #include "mojo/edk/system/ports/name.h"
 #include "mojo/edk/system/system_impl_export.h"
+#include "mojo/edk/system/watcher.h"
 #include "mojo/public/c/system/buffer.h"
 #include "mojo/public/c/system/data_pipe.h"
 #include "mojo/public/c/system/message_pipe.h"
@@ -64,6 +65,14 @@ class MOJO_SYSTEM_IMPL_EXPORT Dispatcher
   virtual Type GetType() const = 0;
   virtual MojoResult Close() = 0;
 
+  ///////////// Watch API ////////////////////
+
+  virtual MojoResult Watch(MojoHandleSignals signals,
+                           const Watcher::WatchCallback& callback,
+                           uintptr_t context);
+
+  virtual MojoResult CancelWatch(uintptr_t context);
+
   ///////////// Message pipe API /////////////
 
   virtual MojoResult WriteMessage(const void* bytes,