Expose if we are using swiftshader via WebGraphicsContext3DProvider.

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

Index: third_party/WebKit/Source/platform/graphics/gpu/DrawingBufferTest.cpp
diff --git a/third_party/WebKit/Source/platform/graphics/gpu/DrawingBufferTest.cpp b/third_party/WebKit/Source/platform/graphics/gpu/DrawingBufferTest.cpp
index 4aa5e5f6f2a85cbcf432db5c421fdb5f238426c3..d2a35c5bd6ade7901e46bf400e7a825f9c41930b 100644
--- a/third_party/WebKit/Source/platform/graphics/gpu/DrawingBufferTest.cpp
+++ b/third_party/WebKit/Source/platform/graphics/gpu/DrawingBufferTest.cpp
@@ -249,13 +249,12 @@ public:
     }
 
     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)>) {}