Remove unused instance tree related member variable

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 242 matching lines @@
 
 void EventHandler::clear()
 {
     m_hoverTimer.stop();
     m_cursorUpdateTimer.stop();
     m_fakeMouseMoveEventTimer.stop();
     m_activeIntervalTimer.stop();
     m_resizeScrollableArea = 0;
     m_nodeUnderMouse = nullptr;
     m_lastNodeUnderMouse = nullptr;
-    m_instanceUnderMouse = nullptr;
     m_lastInstanceUnderMouse = nullptr;
     m_lastMouseMoveEventSubframe = nullptr;
     m_lastScrollbarUnderMouse = nullptr;
     m_clickCount = 0;
     m_clickNode = nullptr;
     m_frameSetBeingResized = nullptr;
     m_dragTarget = nullptr;
     m_shouldOnlyFireDragOverEvent = false;
     m_mousePositionIsUnknown = true;
     m_lastKnownMousePosition = IntPoint();
@@ skipping 1553 matching lines @@
 
     // If we're capturing, we always go right to that node.
     if (m_capturingMouseEventsNode)
         result = m_capturingMouseEventsNode.get();
     else {
         // If the target node is a text node, dispatch on the parent node - rdar://4196646
         if (result && result->isTextNode())
             result = NodeRenderingTraversal::parent(result);
     }
     m_nodeUnderMouse = result;
-    m_instanceUnderMouse = instanceAssociatedWithShadowTreeElement(result);
 
     // <use> shadow tree elements may have been recloned, update node under mouse in any case
     if (m_lastInstanceUnderMouse) {
         SVGElement* lastCorrespondingElement = m_lastInstanceUnderMouse->correspondingElement();
         SVGElement* lastCorrespondingUseElement = m_lastInstanceUnderMouse->correspondingUseElement();
 
         if (lastCorrespondingElement && lastCorrespondingUseElement) {
             HashSet<SVGElementInstance*> instances = lastCorrespondingElement->instancesForElement();
 
             // Locate the recloned shadow tree element for our corresponding instance
@@ skipping 1936 matching lines @@
 unsigned EventHandler::accessKeyModifiers()
 {
 #if OS(MACOSX)
     return PlatformEvent::CtrlKey | PlatformEvent::AltKey;
 #else
     return PlatformEvent::AltKey;
 #endif
 }
 
 } // namespace WebCore