Deal gracefully with null {GraphicsContext,SkPictureBuilder}.endRecording() results.

third_party/WebKit/Source/core/layout/svg/LayoutSVGResourcePattern.h

 /*
  * 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 36 matching lines @@
     void removeAllClientsFromCache(bool markForInvalidation = true) override;
     void removeClientFromCache(LayoutObject*, bool markForInvalidation = true) override;
 
     SVGPaintServer preparePaintServer(const LayoutObject&) override;
 
     static const LayoutSVGResourceType s_resourceType = PatternResourceType;
     LayoutSVGResourceType resourceType() const override { return s_resourceType; }
 
 private:
     PassOwnPtr<PatternData> buildPatternData(const LayoutObject&);
+    // Returns a picture to paint the pattern, or nullptr if the picture couldn't be created.
+    // Pictures should only fail creation in certain testing situations.
     PassRefPtr<SkPicture> asPicture(const FloatRect& tile, const AffineTransform&) const;
     PatternData* patternForLayoutObject(const LayoutObject&);
 
     const LayoutSVGResourceContainer* resolveContentElement() const;
 
     bool m_shouldCollectPatternAttributes : 1;
 #if ENABLE(OILPAN)
     Persistent<PatternAttributesWrapper> m_attributesWrapper;
 
     PatternAttributes& mutableAttributes() { return m_attributesWrapper->attributes(); }
@@ skipping 10 matching lines @@
     // Hence, we need one Pattern shader per client. The display list OTOH is the same => we
     // should be able to cache a single display list per LayoutSVGResourcePattern + one
     // Pattern(shader) for each client -- this would avoid re-recording when multiple clients
     // share the same pattern.
     HashMap<const LayoutObject*, OwnPtr<PatternData>> m_patternMap;
 };
 
 } // namespace blink
 
 #endif