Mark the ET_MOUSE_MOVED created from a pointer grab as synthesized.

ui/events/x/events_x_utils.cc

Index: ui/events/x/events_x_utils.cc
diff --git a/ui/events/x/events_x_utils.cc b/ui/events/x/events_x_utils.cc
index fa37616887cec9592fa12b42e0aecdb70c18de07..af656b4128087b57bf9f4a55ca92540d2e04f01c 100644
--- a/ui/events/x/events_x_utils.cc
+++ b/ui/events/x/events_x_utils.cc
@@ -474,6 +474,9 @@ int EventFlagsFromXEvent(const XEvent& xev) {
       return flags;
     }
     case EnterNotify:
+      // EnterNotify creates ET_MOUSE_MOVED. Mark as synthesized as this is not
+      // a real mouse move event.
+      return GetEventFlagsFromXState(xev.xcrossing.state) | EF_IS_SYNTHESIZED;
     case LeaveNotify:
       return GetEventFlagsFromXState(xev.xcrossing.state);
     case MotionNotify: