Have srcset respond to viewport changes

Source/core/css/MediaQueryList.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 19 matching lines @@
 PassRefPtrWillBeRawPtr<MediaQueryList> MediaQueryList::create(PassRefPtrWillBeRawPtr<MediaQueryMatcher> matcher, PassRefPtrWillBeRawPtr<MediaQuerySet> media)
 {
     return adoptRefWillBeNoop(new MediaQueryList(matcher, media));
 }
 
 MediaQueryList::MediaQueryList(PassRefPtrWillBeRawPtr<MediaQueryMatcher> matcher, PassRefPtrWillBeRawPtr<MediaQuerySet> media)
     : m_matcher(matcher)
     , m_media(media)
     , m_matchesDirty(true)
     , m_matches(false)
+    , m_alwaysUpdate(false)
 {
     m_matcher->addMediaQueryList(this);
     updateMatches();
 }
 
 MediaQueryList::~MediaQueryList()
 {
 #if !ENABLE(OILPAN)
     m_matcher->removeMediaQueryList(this);
 #endif
@@ skipping 42 matching lines @@
     if (!updateMatches())
         return;
     for (ListenerList::const_iterator it = m_listeners.begin(), end = m_listeners.end(); it != end; ++it) {
         listenersToNotify->append(*it);
     }
 }
 
 bool MediaQueryList::updateMatches()
 {
     m_matchesDirty = false;
-    if (m_matches != m_matcher->evaluate(m_media.get())) {
+    if (m_alwaysUpdate || m_matches != m_matcher->evaluate(m_media.get())) {
         m_matches = !m_matches;
         return true;
     }
     return false;
 }
 
 bool MediaQueryList::matches()
 {
     updateMatches();
     return m_matches;
 }
 
 void MediaQueryList::trace(Visitor* visitor)
 {
     visitor->trace(m_matcher);
     visitor->trace(m_media);
     visitor->trace(m_listeners);
 }
 
 }