Expose if we are using swiftshader via WebGraphicsContext3DProvider.

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 370 matching lines @@
     GLboolean m_colorMask[4];
 
     std::unique_ptr<WebGraphicsContext3DProvider> m_contextProvider;
     // Lifetime is tied to the m_contextProvider.
     gpu::gles2::GLES2Interface* m_gl;
     std::unique_ptr<Extensions3DUtil> m_extensionsUtil;
     IntSize m_size = { -1, -1 };
     const bool m_discardFramebufferSupported;
     const bool m_wantAlphaChannel;
     const bool m_premultipliedAlpha;
+    const bool m_softwareRendering;
     bool m_hasImplicitStencilBuffer = false;
     bool m_storageTextureSupported = false;
     struct FrontBufferInfo {
         gpu::Mailbox mailbox;
         gpu::SyncToken produceSyncToken;
         TextureInfo texInfo;
     };
     FrontBufferInfo m_frontColorBuffer;
 
     std::unique_ptr<WTF::Closure> m_newMailboxCallback;
@@ skipping 77 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