[mojo-edk] Expose notification source to MojoWatch callbacks

mojo/public/c/system/types.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // This file contains types and constants/macros common to different Mojo system
 // APIs.
 //
 // Note: This header should be compilable as C.
 
 #ifndef MOJO_PUBLIC_C_SYSTEM_TYPES_H_
@@ skipping 164 matching lines @@
 // Note: This struct is not extensible (and only has 32-bit quantities), so it's
 // 32-bit-aligned.
 MOJO_STATIC_ASSERT(MOJO_ALIGNOF(int32_t) == 4, "int32_t has weird alignment");
 struct MOJO_ALIGNAS(4) MojoHandleSignalsState {
   MojoHandleSignals satisfied_signals;
   MojoHandleSignals satisfiable_signals;
 };
 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_