Define step timing function for the cc animation framework.

public/platform/WebFilterAnimationCurve.h

Index: public/platform/WebFilterAnimationCurve.h
diff --git a/public/platform/WebFilterAnimationCurve.h b/public/platform/WebFilterAnimationCurve.h
index aad09702bffd4f6a25530d96c3661f44ab3e53d4..fbacae45814b14402bcdee6ada2e2d8afe9ae6a9 100644
--- a/public/platform/WebFilterAnimationCurve.h
+++ b/public/platform/WebFilterAnimationCurve.h
@@ -47,6 +47,8 @@ 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 WebFilterKeyframe&, double x1, double y1, double x2, double y2) = 0;
+    // Adds the keyframe with a steps timing function.
+    virtual void add(const WebFilterKeyframe&, int steps, float stepsStartOffset) = 0;
 };
 
 } // namespace blink