Implement Middle Click Autoscroll on all platforms not just Windows

third_party/WebKit/Source/core/input/EventHandler.h

 /*
  * Copyright (C) 2006, 2007, 2009, 2010, 2011 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 78 matching lines @@
     WTF_MAKE_NONCOPYABLE(EventHandler);
 public:
     explicit EventHandler(LocalFrame*);
     ~EventHandler();
     DECLARE_TRACE();
 
     void clear();
     void nodeWillBeRemoved(Node&);
 
     void updateSelectionForMouseDrag();
-
-#if OS(WIN)
     void startPanScrolling(LayoutObject*);
-#endif
 
     // TODO(nzolghadr): Some of the APIs in this class only forward the action
     // to the corresponding Manager class. We need to investigate whether it is
     // better to expose the manager instance itself later or can the access to
     // those APIs be more limited or removed.
 
     void stopAutoscroll();
 
     void dispatchFakeMouseMoveEventSoon();
     void dispatchFakeMouseMoveEventSoonInQuad(const FloatQuad&);
@@ skipping 301 matching lines @@
     // firing for the current gesture sequence (i.e. until next GestureTapDown).
     bool m_suppressMouseEventsFromGestures;
 
     // TODO(nzolghadr): Temporary until further refactoring
     friend GestureManager;
 };
 
 } // namespace blink
 
 #endif // EventHandler_h