Have srcset respond to viewport changes

Source/core/css/MediaQueryMatcher.h

Index: Source/core/css/MediaQueryMatcher.h
diff --git a/Source/core/css/MediaQueryMatcher.h b/Source/core/css/MediaQueryMatcher.h
index f33252272f92f23542e9f13df8e80eb712c9afd0..0a661cea218f0e2950a9e6f9b984e7f2d75ba52a 100644
--- a/Source/core/css/MediaQueryMatcher.h
+++ b/Source/core/css/MediaQueryMatcher.h
@@ -47,9 +47,13 @@ public:
     void addMediaQueryList(MediaQueryList*);
     void removeMediaQueryList(MediaQueryList*);
 
+    void addViewportListener(MediaQueryListListener*);
+    void removeViewportListener(MediaQueryListListener*);
+
     PassRefPtrWillBeRawPtr<MediaQueryList> matchMedia(const String&);
 
     void mediaFeaturesChanged();
+    void viewportChanged();
     bool evaluate(const MediaQuerySet*);
 
     void trace(Visitor*);
@@ -64,6 +68,9 @@ private:
 
     typedef WillBeHeapLinkedHashSet<RawPtrWillBeWeakMember<MediaQueryList> > MediaQueryListSet;
     MediaQueryListSet m_mediaLists;
+
+    typedef WillBeHeapLinkedHashSet<RawPtrWillBeWeakMember<MediaQueryListListener> > ViewportListenerSet;
+    ViewportListenerSet m_viewportListeners;
 };
 
 }