Make lost context callback a base::Closure thru the WGC3DProvider.

third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.h

 /*
  * Copyright (c) 2010, 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 134 matching lines @@
     void markContentsChanged();
     void setBufferClearNeeded(bool);
     bool bufferClearNeeded() const;
     void setIsHidden(bool);
     void setFilterQuality(SkFilterQuality);
 
     WebLayer* platformLayer();
 
     WebGraphicsContext3D* context();
     gpu::gles2::GLES2Interface* contextGL();
+    WebGraphicsContext3DProvider* contextProvider();
 
     // Returns the actual context attributes for this drawing buffer which may differ from the
     // requested context attributes due to implementation limits.
     WebGraphicsContext3D::Attributes getActualAttributes() const { return m_actualAttributes; }
 
     // WebExternalTextureLayerClient implementation.
     bool prepareMailbox(WebExternalTextureMailbox*, WebExternalBitmap*) override;
     void mailboxReleased(const WebExternalTextureMailbox&, bool lostResource = false) override;
 
     // Destroys the TEXTURE_2D binding for the owned context
@@ skipping 203 matching lines @@
     // used to resize the Canvas.
     SkBitmap m_resizingBitmap;
 
     // Used to flip a bitmap vertically.
     Vector<uint8_t> m_scanline;
 };
 
 } // namespace blink
 
 #endif // DrawingBuffer_h