Have srcset respond to viewport changes

Source/core/css/MediaQueryMatcher.cpp

 /*
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies)
  *
  *  This library is free software; you can redistribute it and/or
  *  modify it under the terms of the GNU Library General Public
  *  License as published by the Free Software Foundation; either
  *  version 2 of the License, or (at your option) any later version.
  *
  *  This library is distributed in the hope that it will be useful,
  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 82 matching lines @@
     m_mediaLists.add(query);
 }
 
 void MediaQueryMatcher::removeMediaQueryList(MediaQueryList* query)
 {
     if (!m_document)
         return;
     m_mediaLists.remove(query);
 }
 
+void MediaQueryMatcher::addViewportListener(MediaQueryListListener* listener)
+{
+    if (!m_document)
+        return;
+    m_viewportListeners.add(listener);
+}
+
+void MediaQueryMatcher::removeViewportListener(MediaQueryListListener* listener)
+{
+    if (!m_document)
+        return;
+    m_viewportListeners.remove(listener);
+}
+
 void MediaQueryMatcher::mediaFeaturesChanged()
 {
     if (!m_document)
         return;
 
     WillBeHeapVector<RefPtrWillBeMember<MediaQueryListListener> > listenersToNotify;
     for (MediaQueryListSet::iterator it = m_mediaLists.begin(); it != m_mediaLists.end(); ++it)
         (*it)->mediaFeaturesChanged(&listenersToNotify);
+    m_document->enqueueMediaQueryChangeListeners(listenersToNotify);
+}
+
+void MediaQueryMatcher::viewportChanged()
+{
+    if (!m_document)
+        return;
+
+    WillBeHeapVector<RefPtrWillBeMember<MediaQueryListListener> > listenersToNotify;
+    for (ViewportListenerSet::iterator it = m_viewportListeners.begin(); it != m_viewportListeners.end(); ++it)
+        listenersToNotify.append(*it);
 
     m_document->enqueueMediaQueryChangeListeners(listenersToNotify);
 }
 
 void MediaQueryMatcher::trace(Visitor* visitor)
 {
 #if ENABLE(OILPAN)
     visitor->trace(m_document);
     visitor->trace(m_mediaLists);
 #endif
 }
 
 }