Define step timing function for the cc animation framework.

public/platform/WebTransformAnimationCurve.h

Index: public/platform/WebTransformAnimationCurve.h
diff --git a/public/platform/WebTransformAnimationCurve.h b/public/platform/WebTransformAnimationCurve.h
index 02cc752372c96114c657fb8e6b744c5999b7d12b..072244533dde76c394321c8a32204ddb0d43f869 100644
--- a/public/platform/WebTransformAnimationCurve.h
+++ b/public/platform/WebTransformAnimationCurve.h
@@ -42,6 +42,8 @@ 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 WebTransformKeyframe&, double x1, double y1, double x2, double y2) = 0;
+    // Adds the keyframe with a steps timing function.
+    virtual void add(const WebTransformKeyframe&, int steps, float stepsStartOffset) = 0;
 };
 
 } // namespace blink