Mark the ET_MOUSE_MOVED created from a pointer grab as synthesized.

ui/events/x/events_x_unittest.cc

 // Copyright (c) 2012 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 <X11/XKBlib.h>
 #include <X11/Xlib.h>
 #include <X11/Xutil.h>
 #include <X11/extensions/XInput2.h>
 #include <stddef.h>
 #include <stdint.h>
@@ skipping 171 matching lines @@
   event.xcrossing.type = EnterNotify;
   event.xcrossing.x = 10;
   event.xcrossing.y = 20;
   event.xcrossing.x_root = 110;
   event.xcrossing.y_root = 120;
 
   // Mouse enter events are converted to mouse move events to be consistent with
   // the way views handle mouse enter. See comments for EnterNotify case in
   // ui::EventTypeFromNative for more details.
   EXPECT_EQ(ui::ET_MOUSE_MOVED, ui::EventTypeFromNative(&event));
+  EXPECT_TRUE(ui::EventFlagsFromNative(&event) & ui::EF_IS_SYNTHESIZED);
   EXPECT_EQ(
       "10,20",
       gfx::ToFlooredPoint(ui::EventLocationFromNative(&event)).ToString());
   EXPECT_EQ("110,120", ui::EventSystemLocationFromNative(&event).ToString());
 
   event.xcrossing.type = LeaveNotify;
   event.xcrossing.x = 30;
   event.xcrossing.y = 40;
   event.xcrossing.x_root = 230;
   event.xcrossing.y_root = 240;
@@ skipping 383 matching lines @@
 
   ResetTimestampRolloverCountersForTesting(
       base::MakeUnique<MockTickClock>(0x100000005));
 
   event.xbutton.time = 0xFFFFFFFF;
   EXPECT_EQ(base::TimeDelta::FromMilliseconds(0xFFFFFFFF).ToInternalValue(),
             ui::EventTimeFromNative(&event).ToInternalValue());
 }
 
 }  // namespace ui