Expose if we are using swiftshader via WebGraphicsContext3DProvider.

third_party/WebKit/Source/platform/graphics/gpu/DrawingBufferTest.cpp

 /*
  * 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 231 matching lines @@
 };
 
 class WebGraphicsContext3DProviderForTests : public WebGraphicsContext3DProvider {
 public:
     WebGraphicsContext3DProviderForTests(std::unique_ptr<gpu::gles2::GLES2Interface> gl)
         : m_gl(std::move(gl))
     {
     }
 
     gpu::gles2::GLES2Interface* contextGL() override { return m_gl.get(); }
+    bool isSoftwareRendering() const override { return false; }
+
     // Not used by WebGL code.
     GrContext* grContext() override { return nullptr; }
     bool bindToCurrentThread() override { return false; }
-    gpu::Capabilities getCapabilities()
-    {
-        return gpu::Capabilities();
-    }
+    gpu::Capabilities getCapabilities() override { return gpu::Capabilities(); }
     void setLostContextCallback(WebClosure) {}
     void setErrorMessageCallback(WebFunction<void(const char*, int32_t id)>) {}
 
 private:
     std::unique_ptr<gpu::gles2::GLES2Interface> m_gl;
 };
 
 class DrawingBufferTest : public Test {
 protected:
     void SetUp() override
@@ skipping 510 matching lines @@
     m_drawingBuffer->setIsHidden(true);
     releaseCallback->Run(waitSyncToken, false /* lostResource */);
     // m_drawingBuffer deletes mailbox immediately when hidden.
 
     EXPECT_EQ(waitSyncToken, m_gl->mostRecentlyWaitedSyncToken());
 
     m_drawingBuffer->beginDestruction();
 }
 
 } // namespace blink