Expose if we are using swiftshader via WebGraphicsContext3DProvider.

third_party/WebKit/Source/core/html/HTMLCanvasElement.h

Index: third_party/WebKit/Source/core/html/HTMLCanvasElement.h
diff --git a/third_party/WebKit/Source/core/html/HTMLCanvasElement.h b/third_party/WebKit/Source/core/html/HTMLCanvasElement.h
index d6f413b18f3fc9de81c825da7bc780f84329d7b6..c4a250f28a9f1803e0a1a1c81bf63f7fadf2b363 100644
--- a/third_party/WebKit/Source/core/html/HTMLCanvasElement.h
+++ b/third_party/WebKit/Source/core/html/HTMLCanvasElement.h
@@ -64,6 +64,7 @@ class ImageBuffer;
 class ImageBufferSurface;
 class ImageData;
 class IntSize;
+class WebGraphicsContext3DProvider;
 
 class CanvasRenderingContext2DOrWebGLRenderingContextOrWebGL2RenderingContextOrImageBitmapRenderingContext;
 typedef CanvasRenderingContext2DOrWebGLRenderingContextOrWebGL2RenderingContextOrImageBitmapRenderingContext RenderingContext;
@@ -147,8 +148,6 @@ public:
     bool hasImageBuffer() const { return m_imageBuffer.get(); }
     void discardImageBuffer();
 
-    bool shouldAccelerate(const IntSize&) const;
-
     bool shouldBeDirectComposited() const;
 
     void prepareSurfaceForPaintingIfNeeded() const;
@@ -220,6 +219,8 @@ private:
     static ContextFactoryVector& renderingContextFactories();
     static CanvasRenderingContextFactory* getRenderingContextFactory(int);
 
+    bool shouldAccelerate(const IntSize&, const WebGraphicsContext3DProvider* sharedMainThreadContextProvider) const;
+
     void parseAttribute(const QualifiedName&, const AtomicString&, const AtomicString&) override;
     LayoutObject* createLayoutObject(const ComputedStyle&) override;
     bool areAuthorShadowsAllowed() const override { return false; }