Stop dispatching mouse move events for wheel scrolling in X11.

ui/events/x/events_x.cc

Index: ui/events/x/events_x.cc
diff --git a/ui/events/x/events_x.cc b/ui/events/x/events_x.cc
index 9bf87c0e24c4e4b2a25aeedddf4d00b1340f4d0e..64da7ca6c8626085e4308056c225f829659c9a1f 100644
--- a/ui/events/x/events_x.cc
+++ b/ui/events/x/events_x.cc
@@ -442,6 +442,14 @@ EventType EventTypeFromNative(const base::NativeEvent& native_event) {
             return ET_UMA_DATA;
           if (GetButtonMaskForX2Event(xievent))
             return ET_MOUSE_DRAGGED;
+          if (DeviceDataManagerX11::GetInstance()->HasEventData(
+                  xievent, DeviceDataManagerX11::DT_CMT_SCROLL_X) ||
+              DeviceDataManagerX11::GetInstance()->HasEventData(
+                  xievent, DeviceDataManagerX11::DT_CMT_SCROLL_Y)) {
+            // Don't produce mouse move events for mousewheel scrolls.
+            return ET_UNKNOWN;
+          }
+
           return ET_MOUSE_MOVED;
         }
         case XI_KeyPress: