Make a pen in eraser mode visible thru PointerEvent.buttons

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

 /*
  * Copyright (C) 2001 Peter Kelly (pmk@post.com)
  * Copyright (C) 2001 Tobias Anton (anton@stud.fbi.fh-darmstadt.de)
  * Copyright (C) 2006 Samuel Weinig (sam.weinig@gmail.com)
  * Copyright (C) 2003, 2004, 2005, 2006, 2008 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
@@ skipping 74 matching lines @@
 
     bool fromTouch() const { return m_syntheticEventType == PlatformMouseEvent::FromTouch; }
 
     const AtomicString& interfaceName() const override;
 
     bool isMouseEvent() const override;
     int which() const final;
 
     EventDispatchMediator* createMediator() override;
 
+    // Follows the definition of |buttons| in the PointerEvent Spec:
+    //   https://w3c.github.io/pointerevents/#the-buttons-property
+    // which extends the UI Events Spec definition:
+    //   https://www.w3.org/TR/uievents/#interface-mouseevent
     enum class Buttons : unsigned {
         None = 0,
         Left = 1 << 0,
         Right = 1 << 1,
-        Middle = 1 << 2
+        Middle = 1 << 2,
+        X1 = 1 << 3,
+        X2 = 1 << 4,
+        Eraser = 1 << 5
     };
 
     DECLARE_VIRTUAL_TRACE();
 
 protected:
     MouseEvent(const AtomicString& type, bool canBubble, bool cancelable, AbstractView*,
         int detail, int screenX, int screenY, int windowX, int windowY,
         int movementX, int movementY,
         PlatformEvent::Modifiers, short button, unsigned short buttons,
         EventTarget* relatedTarget,
@@ skipping 30 matching lines @@
     MouseEvent& event() const;
 
     DispatchEventResult dispatchEvent(EventDispatcher&) const override;
 };
 
 DEFINE_EVENT_TYPE_CASTS(MouseEvent);
 
 } // namespace blink
 
 #endif // MouseEvent_h