Expose if we are using swiftshader via WebGraphicsContext3DProvider.

third_party/WebKit/public/platform/WebGraphicsContext3DProvider.h

 /*
  * 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:
  *
  *     * 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 36 matching lines @@
 
 class WebGraphicsContext3DProvider {
 public:
     virtual ~WebGraphicsContext3DProvider() { }
 
     virtual gpu::gles2::GLES2Interface* contextGL() = 0;
     virtual bool bindToCurrentThread() = 0;
     virtual GrContext* grContext() = 0;
     virtual gpu::Capabilities getCapabilities() = 0;
 
+    // Returns true if the context is driven by software emulation of GL. In
+    // this scenario, the compositor would not be using GPU.
+    virtual bool isSoftwareRendering() const = 0;
+
     virtual void setLostContextCallback(WebClosure) = 0;
     virtual void setErrorMessageCallback(WebFunction<void(const char* msg, int32_t id)>) = 0;
 };
 
 } // namespace blink
 
 #endif