Add UMA for selection drag autoscroll.

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

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2006 Alexey Proskuryakov (ap@webkit.org)
  * Copyright (C) 2012 Digia Plc. and/or its subsidiary(-ies)
  *
  * 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
@@ skipping 159 matching lines @@
         stopAutoscroll();
         return;
     }
 
     m_dragAndDropAutoscrollReferencePosition = eventPosition + offset;
 
     if (m_autoscrollType == NoAutoscroll) {
         m_autoscrollType = AutoscrollForDragAndDrop;
         m_autoscrollLayoutObject = scrollable;
         m_dragAndDropAutoscrollStartTime = eventTime;
+        UseCounter::count(m_page->mainFrame(), UseCounter::DragAndDropScrollStart);
         startAutoscroll();
     } else if (m_autoscrollLayoutObject != scrollable) {
         m_dragAndDropAutoscrollStartTime = eventTime;
         m_autoscrollLayoutObject = scrollable;
     }
 }
 
 void AutoscrollController::handleMouseReleaseForMiddleClickAutoscroll(LocalFrame* frame, const PlatformMouseEvent& mouseEvent)
 {
     DCHECK(RuntimeEnabledFeatures::middleClickAutoscrollEnabled());
@@ skipping 109 matching lines @@
     } else if (east) {
         view->setCursor(eastPanningCursor());
     } else if (west) {
         view->setCursor(westPanningCursor());
     } else {
         view->setCursor(middlePanningCursor());
     }
 }
 
 } // namespace blink