[mojo-edk] Add MojoWatch and MojoCancelWatch APIs

mojo/edk/system/message_pipe_dispatcher.cc

Index: mojo/edk/system/message_pipe_dispatcher.cc
diff --git a/mojo/edk/system/message_pipe_dispatcher.cc b/mojo/edk/system/message_pipe_dispatcher.cc
index c7b4a32da6bad0e0cbea48ddc8b3e60683a01966..6bec9bb67fa00b3205fc266023eb97c4e905304a 100644
--- a/mojo/edk/system/message_pipe_dispatcher.cc
+++ b/mojo/edk/system/message_pipe_dispatcher.cc
@@ -97,6 +97,27 @@ MojoResult MessagePipeDispatcher::Close() {
   return CloseNoLock();
 }
 
+MojoResult MessagePipeDispatcher::Watch(MojoHandleSignals signals,
+                                        const Watcher::WatchCallback& callback,
+                                        uintptr_t context) {
+  base::AutoLock lock(signal_lock_);
+
+  if (port_closed_ || in_transit_)
+    return MOJO_RESULT_INVALID_ARGUMENT;
+
+  return awakables_.AddWatcher(
+      signals, callback, context, GetHandleSignalsStateNoLock());
+}
+
+MojoResult MessagePipeDispatcher::CancelWatch(uintptr_t context) {
+  base::AutoLock lock(signal_lock_);
+
+  if (port_closed_ || in_transit_)
+    return MOJO_RESULT_INVALID_ARGUMENT;
+
+  return awakables_.RemoveWatcher(context);
+}
+
 MojoResult MessagePipeDispatcher::WriteMessage(
     const void* bytes,
     uint32_t num_bytes,