Implement Middle Click Autoscroll on all platforms not just Windows

third_party/WebKit/Source/core/layout/LayoutBox.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2005 Allan Sandfeld Jensen (kde@carewolf.com)
  *           (C) 2005, 2006 Samuel Weinig (sam.weinig@gmail.com)
  * Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2013 Adobe Systems Incorporated. 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
@@ skipping 949 matching lines @@
         adjustedDelta = static_cast<int>(adjustedDelta * sqrt(static_cast<double>(-adjustedDelta))) + 1;
 
     return adjustedDelta;
 }
 
 static inline IntSize adjustedScrollDelta(const IntSize& delta)
 {
     return IntSize(adjustedScrollDelta(delta.width()), adjustedScrollDelta(delta.height()));
 }
 
-void LayoutBox::panScroll(const IntPoint& sourcePoint)
+void LayoutBox::middleClickAutoscroll(const IntPoint& sourcePoint)
 {
     LocalFrame* frame = this->frame();
     if (!frame)
         return;
 
     IntPoint lastKnownMousePosition = frame->eventHandler().lastKnownMousePosition();
 
     // We need to check if the last known mouse position is out of the window. When the mouse is out of the window, the position is incoherent
     static IntPoint previousMousePosition;
     if (lastKnownMousePosition.x() < 0 || lastKnownMousePosition.y() < 0)
         lastKnownMousePosition = previousMousePosition;
     else
         previousMousePosition = lastKnownMousePosition;
 
     IntSize delta = lastKnownMousePosition - sourcePoint;
 
-    if (abs(delta.width()) <= AutoscrollController::noPanScrollRadius) // at the center we let the space for the icon
+    if (abs(delta.width()) <= AutoscrollController::noMiddleClickAutoscrollRadius) // at the center we let the space for the icon
         delta.setWidth(0);
-    if (abs(delta.height()) <= AutoscrollController::noPanScrollRadius)
+    if (abs(delta.height()) <= AutoscrollController::noMiddleClickAutoscrollRadius)
         delta.setHeight(0);
     scroll(ScrollByPixel, FloatSize(adjustedScrollDelta(delta)));
 }
 
 void LayoutBox::scrollByRecursively(const DoubleSize& delta, ScrollOffsetClamping clamp)
 {
     if (delta.isZero())
         return;
 
     bool restrictedByLineClamp = false;
@@ skipping 3845 matching lines @@
         m_rareData->m_snapAreas->remove(&snapArea);
     }
 }
 
 SnapAreaSet* LayoutBox::snapAreas() const
 {
     return m_rareData ? m_rareData->m_snapAreas.get() : nullptr;
 }
 
 } // namespace blink