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 194 matching lines @@
 
     gpu::gles2::GLES2Interface* contextGL();
     WebGraphicsContext3DProvider* contextProvider();
 
     // cc::TextureLayerClient implementation.
     bool PrepareTextureMailbox(
         cc::TextureMailbox* outMailbox,
         std::unique_ptr<cc::SingleReleaseCallback>* outReleaseCallback,
         bool useSharedMemory) override;
 
-    // Callbacks for mailboxes given to the compositor from PrepareTextureMailbox.
-    void gpuMailboxReleased(const gpu::Mailbox&, const gpu::SyncToken&, bool lostResource);
-    void softwareMailboxReleased(std::unique_ptr<cc::SharedBitmap>, const IntSize&, const gpu::SyncToken&, bool lostResource);
-
     // Returns a StaticBitmapImage backed by a texture containing the/ current contents of
     // the front buffer. This is done without any pixel copies. The texture in the ImageBitmap
     // is from the active ContextProvider on the DrawingBuffer.
     PassRefPtr<StaticBitmapImage> transferToStaticBitmapImage();
 
     // Destroys the TEXTURE_2D binding for the owned context
     bool copyToPlatformTexture(gpu::gles2::GLES2Interface*, GLuint texture, GLenum internalFormat,
         GLenum destType, GLint level, bool premultiplyAlpha, bool flipY, SourceDrawingBuffer);
 
     void setPackAlignment(GLint param);
@@ skipping 53 matching lines @@
     struct MailboxInfo : public RefCounted<MailboxInfo> {
         MailboxInfo() = default;
         gpu::Mailbox mailbox;
         TextureInfo textureInfo;
         IntSize size;
 
     private:
         WTF_MAKE_NONCOPYABLE(MailboxInfo);
     };
 
+    bool prepareTextureMailboxInternal(
+        cc::TextureMailbox* outMailbox,
+        std::unique_ptr<cc::SingleReleaseCallback>* outReleaseCallback,
+        bool forceGpuResult);
+
+    // Callbacks for mailboxes given to the compositor from PrepareTextureMailbox.
+    void gpuMailboxReleased(const gpu::Mailbox&, const gpu::SyncToken&, bool lostResource);
+    void softwareMailboxReleased(std::unique_ptr<cc::SharedBitmap>, const IntSize&, const gpu::SyncToken&, bool lostResource);
+
     // The texture parameters to use for a texture that will be backed by a
     // CHROMIUM_image.
     TextureParameters chromiumImageTextureParameters();
 
     // The texture parameters to use for a default texture.
     TextureParameters defaultTextureParameters();
 
     // Creates and binds a texture with the given parameters. Returns 0 on
     // failure, or the newly created texture id on success. The caller takes
     // ownership of the newly created texture.
@@ skipping 79 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