Define step timing function for the cc animation framework.

cc/blink/web_filter_animation_curve_impl.h

Index: cc/blink/web_filter_animation_curve_impl.h
diff --git a/cc/blink/web_filter_animation_curve_impl.h b/cc/blink/web_filter_animation_curve_impl.h
index ea75eb55c579a8a209fde141556768b4adda61e8..de3231694af20a5a5ef993676d403943810dafcb 100644
--- a/cc/blink/web_filter_animation_curve_impl.h
+++ b/cc/blink/web_filter_animation_curve_impl.h
@@ -36,6 +36,10 @@ class WebFilterAnimationCurveImpl : public blink::WebFilterAnimationCurve {
                    double y1,
                    double x2,
                    double y2);
+  virtual void add(const blink::WebFilterKeyframe& keyframe,
+                   int steps,
+                   float steps_start_offset);
+
   virtual void setTimingFunction(TimingFunctionType type);
   virtual void setTimingFunction(double x1, double y1, double x2, double y2);