Correct the (x, y) position of dragstart event initiated by touch event

Source/core/page/EventHandler.cpp

 /*
  * 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
  *    notice, this list of conditions and the following disclaimer.
@@ skipping 2385 matching lines @@
 bool EventHandler::handleGestureLongPress(const PlatformGestureEvent& gestureEvent)
 {
     IntPoint adjustedPoint = gestureEvent.position();
     adjustGesturePosition(gestureEvent, adjustedPoint);
     RefPtr<Frame> subframe = getSubFrameForGestureEvent(adjustedPoint, gestureEvent);
     if (subframe && subframe->eventHandler()->handleGestureLongPress(gestureEvent))
         return true;
 
     m_longTapShouldInvokeContextMenu = false;
     if (m_frame->settings() && m_frame->settings()->touchDragDropEnabled() && m_frame->view()) {
+        PlatformMouseEvent mouseDownEvent(adjustedPoint, gestureEvent.globalPosition(), LeftButton, PlatformEvent::MousePressed, 1,
+            gestureEvent.shiftKey(), gestureEvent.ctrlKey(), gestureEvent.altKey(), gestureEvent.metaKey(), WTF::currentTime());
+        m_mouseDown = mouseDownEvent;
+
         PlatformMouseEvent mouseDragEvent(adjustedPoint, gestureEvent.globalPosition(), LeftButton, PlatformEvent::MouseMoved, 1,
             gestureEvent.shiftKey(), gestureEvent.ctrlKey(), gestureEvent.altKey(), gestureEvent.metaKey(), WTF::currentTime());
         HitTestRequest request(HitTestRequest::ReadOnly | HitTestRequest::DisallowShadowContent);
         MouseEventWithHitTestResults mev = prepareMouseEvent(request, mouseDragEvent);
         m_didStartDrag = false;
         m_mouseDownMayStartDrag = true;
         dragState().m_dragSrc = 0;
         m_mouseDownPos = m_frame->view()->windowToContents(mouseDragEvent.position());
         handleDrag(mev, DontCheckDragHysteresis);
         if (m_didStartDrag) {
@@ skipping 1504 matching lines @@
 unsigned EventHandler::accessKeyModifiers()
 {
 #if OS(DARWIN)
     return PlatformEvent::CtrlKey | PlatformEvent::AltKey;
 #else
     return PlatformEvent::AltKey;
 #endif
 }
 
 } // namespace WebCore