SVG: Moving animating <svg> to other iframe should not crash.

Source/core/svg/SVGDocumentExtensions.cpp

 /*
  * Copyright (C) 2006 Apple Inc. All rights reserved.
  * Copyright (C) 2006 Nikolas Zimmermann <zimmermann@kde.org>
  * Copyright (C) 2007 Rob Buis <buis@kde.org>
  *
  * 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.
  *
@@ skipping 93 matching lines @@
 
 void SVGDocumentExtensions::startAnimations()
 {
     // FIXME: Eventually every "Time Container" will need a way to latch on to some global timer
     // starting animations for a document will do this "latching"
     // FIXME: We hold a ref pointers to prevent a shadow tree from getting removed out from underneath us.
     // In the future we should refactor the use-element to avoid this. See https://webkit.org/b/53704
     WillBeHeapVector<RefPtrWillBeMember<SVGSVGElement> > timeContainers;
     timeContainers.appendRange(m_timeContainers.begin(), m_timeContainers.end());
     WillBeHeapVector<RefPtrWillBeMember<SVGSVGElement> >::iterator end = timeContainers.end();
-    for (WillBeHeapVector<RefPtrWillBeMember<SVGSVGElement> >::iterator itr = timeContainers.begin(); itr != end; ++itr)
-        (*itr)->timeContainer()->begin();
+    for (WillBeHeapVector<RefPtrWillBeMember<SVGSVGElement> >::iterator itr = timeContainers.begin(); itr != end; ++itr) {
+        SMILTimeContainer* timeContainer = (*itr)->timeContainer();
+        if (!timeContainer->isStarted())
+            timeContainer->begin();
+    }
 }
 
 void SVGDocumentExtensions::pauseAnimations()
 {
     WillBeHeapHashSet<RawPtrWillBeMember<SVGSVGElement> >::iterator end = m_timeContainers.end();
     for (WillBeHeapHashSet<RawPtrWillBeMember<SVGSVGElement> >::iterator itr = m_timeContainers.begin(); itr != end; ++itr)
         (*itr)->pauseAnimations();
 }
 
 void SVGDocumentExtensions::dispatchSVGLoadEventToOutermostSVGElements()
@@ skipping 350 matching lines @@
 }
 
 void SVGDocumentExtensions::trace(Visitor* visitor)
 {
     visitor->trace(m_timeContainers);
     visitor->trace(m_svgFontFaceElements);
     visitor->trace(m_pendingSVGFontFaceElementsForRemoval);
 }
 
 }