[SVG] Reinstate RenderSVGResourcePattern's inval-during-paint guard.

Source/core/rendering/svg/RenderSVGResourcePattern.cpp

 /*
  * Copyright (C) 2006 Nikolas Zimmermann <zimmermann@kde.org>
  * Copyright (C) Research In Motion Limited 2010. All rights reserved.
  * Copyright 2014 The Chromium Authors. All rights reserved.
  *
  * 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 44 matching lines @@
 
 void RenderSVGResourcePattern::removeClientFromCache(RenderObject* client, bool markForInvalidation)
 {
     ASSERT(client);
     m_patternMap.remove(client);
     markClientForInvalidation(client, markForInvalidation ? PaintInvalidation : ParentOnlyInvalidation);
 }
 
 PatternData* RenderSVGResourcePattern::patternForRenderer(const RenderObject& object)
 {
-    auto addResult = m_patternMap.add(&object, nullptr);
-    OwnPtr<PatternData>& patternData = addResult.storedValue->value;
+    ASSERT(!m_shouldCollectPatternAttributes);
 
-    if (addResult.isNewEntry)
-        patternData = buildPatternData(object);
+    // FIXME: the double hash lookup is needed to guard against paint-time invalidation
+    // (painting animated images may trigger layout invals which delete our map entry).
+    // Hopefully that will be addressed at some point, and then we can optimize the lookup.
+    if (PatternData* currentData = m_patternMap.get(&object))
+        return currentData;
 
-    ASSERT(!m_shouldCollectPatternAttributes);
-    return patternData.get();
+    return m_patternMap.set(&object, buildPatternData(object)).storedValue->value.get();
 }
 
 PassOwnPtr<PatternData> RenderSVGResourcePattern::buildPatternData(const RenderObject& object)
 {
     // If we couldn't determine the pattern content element root, stop here.
     if (!m_attributes.patternContentElement())
         return nullptr;
 
     // An empty viewBox disables rendering.
     if (m_attributes.hasViewBox() && m_attributes.viewBox().isEmpty())
@@ skipping 84 matching lines @@
     ASSERT(!patternRenderer->needsLayout());
 
     SubtreeContentTransformScope contentTransformScope(contentTransform);
     for (RenderObject* child = patternRenderer->firstChild(); child; child = child->nextSibling())
         SVGRenderingContext::renderSubtree(&recordingContext, child);
 
     return recordingContext.endRecording();
 }
 
 }