Have srcset respond to viewport changes

Source/core/dom/ScriptedAnimationController.cpp

 /*
  * Copyright (C) 2011 Google Inc. All Rights Reserved.
  *
  * 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.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 155 matching lines @@
             InspectorInstrumentation::didFireAnimationFrame(cookie);
             TRACE_EVENT_INSTANT1(TRACE_DISABLED_BY_DEFAULT("devtools.timeline"), "UpdateCounters", "data", InspectorUpdateCountersEvent::data());
         }
     }
 
     m_callbacksToInvoke.clear();
 }
 
 void ScriptedAnimationController::callMediaQueryListListeners()
 {
+    ASSERT(m_mediaQueryListListeners.size());
     MediaQueryListListeners listeners;
     listeners.swap(m_mediaQueryListListeners);
 
     for (MediaQueryListListeners::const_iterator it = listeners.begin(), end = listeners.end();
         it != end; ++it) {
         (*it)->call();
     }
 }
 
 void ScriptedAnimationController::serviceScriptedAnimations(double monotonicTimeNow)
@@ skipping 44 matching lines @@
         return;
 
     if (!m_callbacks.size() && !m_eventQueue.size() && !m_mediaQueryListListeners.size())
         return;
 
     if (FrameView* frameView = m_document->view())
         frameView->scheduleAnimation();
 }
 
 }