Define step timing function for the cc animation framework.

cc/blink/web_float_animation_curve_impl.h

Index: cc/blink/web_float_animation_curve_impl.h
diff --git a/cc/blink/web_float_animation_curve_impl.h b/cc/blink/web_float_animation_curve_impl.h
index 8e5ccd241b745bfc9525a979db391381bae3d588..9fca7bba4b8e3b55c765b25df28c2c83fbd29ca8 100644
--- a/cc/blink/web_float_animation_curve_impl.h
+++ b/cc/blink/web_float_animation_curve_impl.h
@@ -37,6 +37,10 @@ class WebFloatAnimationCurveImpl : public blink::WebFloatAnimationCurve {
                    double y1,
                    double x2,
                    double y2);
+  virtual void add(const blink::WebFloatKeyframe& keyframe,
+                   int steps,
+                   float steps_start_offset);
+
   virtual void setTimingFunction(TimingFunctionType type);
   virtual void setTimingFunction(double x1, double y1, double x2, double y2);