Define step timing function for the cc animation framework.

cc/blink/web_transform_animation_curve_impl.h

Index: cc/blink/web_transform_animation_curve_impl.h
diff --git a/cc/blink/web_transform_animation_curve_impl.h b/cc/blink/web_transform_animation_curve_impl.h
index a4dbe2279893f746d0cf7a4cf9157d842413be19..6dc64b57bf9ed812b3037686a2bd1e94caa4c628 100644
--- a/cc/blink/web_transform_animation_curve_impl.h
+++ b/cc/blink/web_transform_animation_curve_impl.h
@@ -38,6 +38,10 @@ class WebTransformAnimationCurveImpl
                    double y1,
                    double x2,
                    double y2);
+  virtual void add(const blink::WebTransformKeyframe& keyframe,
+                   int steps,
+                   float stepsStartOffset);
+
   virtual void setTimingFunction(TimingFunctionType type);
   virtual void setTimingFunction(double x1, double y1, double x2, double y2);