[mojo-edk] Expose notification source to MojoWatch callbacks

mojo/public/c/system/types.h

Index: mojo/public/c/system/types.h
diff --git a/mojo/public/c/system/types.h b/mojo/public/c/system/types.h
index 4574d7413615eac0a740cfd4925c185d8513e3fd..6d21b12a172aefc805a98354479dd1fd1ceaef52 100644
--- a/mojo/public/c/system/types.h
+++ b/mojo/public/c/system/types.h
@@ -182,4 +182,24 @@ struct MOJO_ALIGNAS(4) MojoHandleSignalsState {
 MOJO_STATIC_ASSERT(sizeof(MojoHandleSignalsState) == 8,
                    "MojoHandleSignalsState has wrong size");
 
+// |MojoWatchNotificationFlags|: Passed to a callback invoked as a result of
+// signals being raised on a handle watched by |MojoWatch()|. May take the
+// following values:
+//   |MOJO_WATCH_NOTIFICATION_FLAG_FROM_SYSTEM| - The callback is being invoked
+//       as a result of a system-level event rather than a direct API call from
+//       user code. This may be used as an indication that user code is safe to
+//       call without fear of reentry.
+
+typedef uint32_t MojoWatchNotificationFlags;
+
+#ifdef __cplusplus
+const MojoWatchNotificationFlags MOJO_WATCH_NOTIFICATION_FLAG_NONE = 0;
+const MojoWatchNotificationFlags MOJO_WATCH_NOTIFICATION_FLAG_FROM_SYSTEM =
+    1 << 0;
+#else
+#define MOJO_WATCH_NOTIFICATION_FLAG_NONE ((MojoWatchNotificationFlags)0)
+#define MOJO_WATCH_NOTIFICATION_FLAG_FROM_SYSTEM \
+    ((MojoWatchNotificationFlags)1 << 0);
+#endif
+
 #endif  // MOJO_PUBLIC_C_SYSTEM_TYPES_H_