Implement Middle Click Autoscroll on all platforms not just Windows

third_party/WebKit/Source/core/page/AutoscrollController.h

Index: third_party/WebKit/Source/core/page/AutoscrollController.h
diff --git a/third_party/WebKit/Source/core/page/AutoscrollController.h b/third_party/WebKit/Source/core/page/AutoscrollController.h
index 3c19a2ee9b1e362d62b9c41966fb19bec3c426eb..4f67c621b2b9aabd4264d4891af3a0101927fa11 100644
--- a/third_party/WebKit/Source/core/page/AutoscrollController.h
+++ b/third_party/WebKit/Source/core/page/AutoscrollController.h
@@ -44,10 +44,8 @@ enum AutoscrollType {
     NoAutoscroll,
     AutoscrollForDragAndDrop,
     AutoscrollForSelection,
-#if OS(WIN)
     AutoscrollForPanCanStop,
     AutoscrollForPan,
-#endif
 };
 
 // AutscrollController handels autoscroll and pan scroll for EventHandler.
@@ -61,25 +59,21 @@ public:
     void animate(double monotonicFrameBeginTime);
     bool autoscrollInProgress() const;
     bool autoscrollInProgress(const LayoutBox*) const;
-    bool panScrollInProgress() const;
+    bool middleClickAutoscrollInProgress() const;
     void startAutoscrollForSelection(LayoutObject*);
     void stopAutoscroll();
     void stopAutoscrollIfNeeded(LayoutObject*);
     void updateAutoscrollLayoutObject();
     void updateDragAndDrop(Node* targetNode, const IntPoint& eventPosition, double eventTime);
-#if OS(WIN)
     void handleMouseReleaseForPanScrolling(LocalFrame*, const PlatformMouseEvent&);
     void startPanScrolling(LayoutBox*, const IntPoint&);
-#endif
 
 private:
     explicit AutoscrollController(Page&);
 
     void startAutoscroll();
 
-#if OS(WIN)
     void updatePanScrollState(FrameView*, const IntPoint& lastKnownMousePosition);
-#endif
 
     Member<Page> m_page;
     LayoutBox* m_autoscrollLayoutObject;
@@ -87,9 +81,7 @@ private:
     AutoscrollType m_autoscrollType;
     IntPoint m_dragAndDropAutoscrollReferencePosition;
     double m_dragAndDropAutoscrollStartTime;
-#if OS(WIN)
-    IntPoint m_panScrollStartPos;
-#endif
+    IntPoint m_middleClickAutoscrollStartPos;
 };
 
 } // namespace blink