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

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

 /*
  * Copyright (C) Research In Motion Limited 2009-2010. 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.
  *
  * This library is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 32 matching lines @@
     void removeClientFromCache(LayoutObject*, bool markForInvalidation = true) override;
 
     FloatRect resourceBoundingBox(const LayoutObject*);
 
     SVGUnitTypes::SVGUnitType maskUnits() const { return toSVGMaskElement(element())->maskUnits()->currentValue()->enumValue(); }
     SVGUnitTypes::SVGUnitType maskContentUnits() const { return toSVGMaskElement(element())->maskContentUnits()->currentValue()->enumValue(); }
 
     static const LayoutSVGResourceType s_resourceType = MaskerResourceType;
     LayoutSVGResourceType resourceType() const override { return s_resourceType; }
 
+    // Returns a picture to paint the contents of the mask, or nullptr if the picture couldn't be created.
+    // Pictures should only fail creation in certain testing situations.
     PassRefPtr<const SkPicture> createContentPicture(AffineTransform&, const FloatRect&, GraphicsContext&);
 
 private:
     void calculateMaskContentPaintInvalidationRect();
 
     RefPtr<const SkPicture> m_maskContentPicture;
     FloatRect m_maskContentBoundaries;
 };
 
 DEFINE_LAYOUT_SVG_RESOURCE_TYPE_CASTS(LayoutSVGResourceMasker, MaskerResourceType);
 
 } // namespace blink
 
 #endif