Fix GeneratedImage::drawPattern() use of SkPictureBuilder.

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

 /*
  * Copyright (C) 2003, 2004, 2005, 2006, 2009 Apple Inc. All rights reserved.
  * 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.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 246 matching lines @@
 
 #if DCHECK_IS_ON()
   DCHECK_GT(m_layerCount--, 0);
 #endif
 }
 
 void GraphicsContext::beginRecording(const FloatRect& bounds) {
   if (contextDisabled())
     return;
 
+  DCHECK(!m_canvas);
   m_canvas = m_pictureRecorder.beginRecording(bounds, nullptr);
   if (m_hasMetaData)
     skia::GetMetaData(*m_canvas) = m_metaData;
 }
 
 namespace {
 
 sk_sp<SkPicture> createEmptyPicture() {
   SkPictureRecorder recorder;
   recorder.beginRecording(SkRect::MakeEmpty(), nullptr);
@@ skipping 1135 matching lines @@
   static const SkPMColor colors[] = {
       SkPreMultiplyARGB(0x60, 0xFF, 0x00, 0x00),  // More transparent red
       SkPreMultiplyARGB(0x60, 0xC0, 0xC0, 0xC0)   // More transparent gray
   };
 
   return colors[index];
 }
 #endif
 
 }  // namespace blink