Fix button event on mouse events.

third_party/WebKit/Source/core/events/MouseEvent.cpp

Index: third_party/WebKit/Source/core/events/MouseEvent.cpp
diff --git a/third_party/WebKit/Source/core/events/MouseEvent.cpp b/third_party/WebKit/Source/core/events/MouseEvent.cpp
index ace0d091e15826f7c909f3850f520f6463d59ada..249ff6911f64d52ac64b89acb70edf682f6b541d 100644
--- a/third_party/WebKit/Source/core/events/MouseEvent.cpp
+++ b/third_party/WebKit/Source/core/events/MouseEvent.cpp
@@ -78,6 +78,19 @@ const LayoutObject* FindTargetLayoutObject(Node*& target_node) {
   return layout_object;
 }
 
+unsigned short WebPointerPropertiesButtonToButton(
+    const AtomicString& event_name,
+    WebPointerProperties::Button button) {
+  if (event_name == EventTypeNames::mousemove ||
+      event_name == EventTypeNames::mouseleave ||
+      event_name == EventTypeNames::mouseenter ||
+      event_name == EventTypeNames::mouseover ||
+      event_name == EventTypeNames::mouseout) {
+    return 0;
+  }
+  return static_cast<unsigned short>(button);
+}
+
 }  // namespace
 
 MouseEvent* MouseEvent::Create(ScriptState* script_state,
@@ -173,7 +186,7 @@ MouseEvent::MouseEvent(const AtomicString& event_type,
       screen_location_(event.PositionInScreen().x, event.PositionInScreen().y),
       movement_delta_(FlooredIntPoint(event.MovementInRootFrame())),
       position_type_(PositionType::kPosition),
-      button_(static_cast<short>(event.button)),
+      button_(WebPointerPropertiesButtonToButton(event_type, event.button)),
       buttons_(WebInputEventModifiersToButtons(event.GetModifiers())),
       related_target_(related_target),
       synthetic_event_type_(event.FromTouch() ? kFromTouch