Prevent default actions for JS-generated mouse events other than click

Source/core/events/MouseEvent.h

Index: Source/core/events/MouseEvent.h
diff --git a/Source/core/events/MouseEvent.h b/Source/core/events/MouseEvent.h
index 3416c30b5e1c9153015e3374f72711e9c0391b12..a845199a61a855ae1e70b239d93c564d9fd11692 100644
--- a/Source/core/events/MouseEvent.h
+++ b/Source/core/events/MouseEvent.h
@@ -79,6 +79,9 @@ public:
 
     bool fromTouch() const { return m_syntheticEventType == PlatformMouseEvent::FromTouch; }
 
+    bool fromScript() const { return m_syntheticEventType == PlatformMouseEvent::FromScript; }
+    void setFromScript() { m_syntheticEventType = PlatformMouseEvent::FromScript; }
+
     virtual const AtomicString& interfaceName() const override;
 
     virtual bool isMouseEvent() const override;
@@ -121,16 +124,13 @@ private:
 
 class MouseEventDispatchMediator final : public EventDispatchMediator {
 public:
-    enum MouseEventType { SyntheticMouseEvent, NonSyntheticMouseEvent};
-    static PassRefPtrWillBeRawPtr<MouseEventDispatchMediator> create(PassRefPtrWillBeRawPtr<MouseEvent>, MouseEventType = NonSyntheticMouseEvent);
+    static PassRefPtrWillBeRawPtr<MouseEventDispatchMediator> create(PassRefPtrWillBeRawPtr<MouseEvent>);
 
 private:
-    explicit MouseEventDispatchMediator(PassRefPtrWillBeRawPtr<MouseEvent>, MouseEventType);
+    explicit MouseEventDispatchMediator(PassRefPtrWillBeRawPtr<MouseEvent>);
     MouseEvent& event() const;
 
     virtual bool dispatchEvent(EventDispatcher&) const override;
-    bool isSyntheticMouseEvent() const { return m_mouseEventType == SyntheticMouseEvent; }
-    MouseEventType m_mouseEventType;
 };
 
 DEFINE_EVENT_TYPE_CASTS(MouseEvent);