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

third_party/WebKit/Source/platform/graphics/GraphicsContext.h

 /*
  * Copyright (C) 2003, 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2008-2009 Torch Mobile, Inc.
  * Copyright (C) 2013 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.
@@ skipping 193 matching lines @@
     // beginLayer()/endLayer() behaves like save()/restore() for CTM and clip states.
     // Apply SkXfermode::Mode when the layer is composited on the backdrop (i.e. endLayer()).
     void beginLayer(float opacity = 1.0f, SkXfermode::Mode = SkXfermode::kSrcOver_Mode,
         const FloatRect* = 0, ColorFilter = ColorFilterNone, SkImageFilter* = 0);
     void endLayer();
 
     // Instead of being dispatched to the active canvas, draw commands following beginRecording()
     // are stored in a display list that can be replayed at a later time. Pass in the bounding
     // rectangle for the content in the list.
     void beginRecording(const FloatRect&);
+    // Returns a picture with any recorded draw commands since the prerequisite call to beginRecording(),
+    // or nullptr if the canvas is disabled.

[chrishtr, 2016/03/29 22:42:23]

add the second sentence

[wkorman, 2016/03/29 22:52:02]

Done, more specific phrasing here since this is the source of it all, as it
were.

     PassRefPtr<SkPicture> endRecording();
 
     void setShadow(const FloatSize& offset, float blur, const Color&,
         DrawLooperBuilder::ShadowTransformMode = DrawLooperBuilder::ShadowRespectsTransforms,
         DrawLooperBuilder::ShadowAlphaMode = DrawLooperBuilder::ShadowRespectsAlpha, ShadowMode = DrawShadowAndForeground);
 
     // It is assumed that this draw looper is used only for shadows
     // (i.e. a draw looper is set if and only if there is a shadow).
     // The builder passed into this method will be destroyed.
     void setDrawLooper(PassOwnPtr<DrawLooperBuilder>);
@@ skipping 146 matching lines @@
 
     float m_deviceScaleFactor;
 
     unsigned m_printing : 1;
     unsigned m_hasMetaData : 1;
 };
 
 } // namespace blink
 
 #endif // GraphicsContext_h