Expose if we are using swiftshader via WebGraphicsContext3DProvider.

third_party/WebKit/public/platform/Platform.h

Index: third_party/WebKit/public/platform/Platform.h
diff --git a/third_party/WebKit/public/platform/Platform.h b/third_party/WebKit/public/platform/Platform.h
index 1a173a2a6033ee74a2c5ffda941960f43f562126..06accdca817323dba9bff914f103e0ac4b70d91d 100644
--- a/third_party/WebKit/public/platform/Platform.h
+++ b/third_party/WebKit/public/platform/Platform.h
@@ -461,13 +461,6 @@ public:
 
     virtual std::unique_ptr<cc::SharedBitmap> allocateSharedBitmap(const WebSize& size) { return nullptr; }
 
-    // Returns true if the platform is capable of producing an offscreen context suitable for accelerating 2d canvas.
-    // This will return false if the platform cannot promise that contexts will be preserved across operations like
-    // locking the screen or if the platform cannot provide a context with suitable performance characteristics.
-    //
-    // This value must be checked again after a context loss event as the platform's capabilities may have changed.
-    virtual bool canAccelerate2dCanvas() { return false; }
-
     virtual bool isThreadedCompositingEnabled() { return false; }
     virtual bool isThreadedAnimationEnabled() { return true; }