Mark the ET_MOUSE_MOVED created from a pointer grab as synthesized.

ui/events/x/events_x_utils.cc

 // Copyright (c) 2016 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.
 
 #include "ui/events/x/events_x_utils.h"
 
 #include <stddef.h>
 #include <string.h>
 #include <X11/extensions/XInput.h>
 #include <X11/extensions/XInput2.h>
@@ skipping 456 matching lines @@
     }
     case ButtonPress:
     case ButtonRelease: {
       int flags = GetEventFlagsFromXState(xev.xbutton.state);
       const EventType type = EventTypeFromXEvent(xev);
       if (type == ET_MOUSE_PRESSED || type == ET_MOUSE_RELEASED)
         flags |= GetEventFlagsForButton(xev.xbutton.button);
       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:
       return GetEventFlagsFromXState(xev.xmotion.state);
     case GenericEvent: {
       XIDeviceEvent* xievent = static_cast<XIDeviceEvent*>(xev.xcookie.data);
 
       switch (xievent->evtype) {
         case XI_TouchBegin:
         case XI_TouchUpdate:
@@ skipping 322 matching lines @@
 }
 
 void ResetTimestampRolloverCountersForTesting(
     std::unique_ptr<base::TickClock> tick_clock) {
   g_last_seen_timestamp_ms = 0;
   g_rollover_ms = 0;
   SetEventTickClockForTesting(std::move(tick_clock));
 }
 
 }  // namespace ui