Define step timing function for the cc animation framework.

public/platform/WebFloatAnimationCurve.h

Index: public/platform/WebFloatAnimationCurve.h
diff --git a/public/platform/WebFloatAnimationCurve.h b/public/platform/WebFloatAnimationCurve.h
index 7c365c759758a511823684d8bc42c14121a9a400..15397deaac16fbf341f120f36adbef45dd94156f 100644
--- a/public/platform/WebFloatAnimationCurve.h
+++ b/public/platform/WebFloatAnimationCurve.h
@@ -43,6 +43,8 @@ public:
     // Adds the keyframe with a custom, bezier timing function. Note, it is
     // assumed that x0 = y0 = 0, and x3 = y3 = 1.
     virtual void add(const WebFloatKeyframe&, double x1, double y1, double x2, double y2) = 0;
+    // Adds the keyframe with a steps timing function.
+    virtual void add(const WebFloatKeyframe&, int steps, float stepsStartOffset) = 0;
 
     virtual float getValue(double time) const = 0;
 };