Define step timing function for the cc animation framework.

cc/blink/web_float_animation_curve_impl.cc

Index: cc/blink/web_float_animation_curve_impl.cc
diff --git a/cc/blink/web_float_animation_curve_impl.cc b/cc/blink/web_float_animation_curve_impl.cc
index d85f57ce96859023edbc2f0561f4322fecd595af..ca5b5d0446394bda8ff805a3f53a4d080a3c0e21 100644
--- a/cc/blink/web_float_animation_curve_impl.cc
+++ b/cc/blink/web_float_animation_curve_impl.cc
@@ -46,6 +46,14 @@ void WebFloatAnimationCurveImpl::add(const WebFloatKeyframe& keyframe,
       cc::CubicBezierTimingFunction::Create(x1, y1, x2, y2)));
 }
 
+void WebFloatAnimationCurveImpl::add(const WebFloatKeyframe& keyframe,
+                                     int steps,
+                                     float steps_start_offset) {
+  curve_->AddKeyframe(cc::FloatKeyframe::Create(
+      base::TimeDelta::FromSecondsD(keyframe.time), keyframe.value,
+      cc::StepsTimingFunction::Create(steps, steps_start_offset)));
+}
+
 void WebFloatAnimationCurveImpl::setTimingFunction(TimingFunctionType type) {
   curve_->SetTimingFunction(CreateTimingFunction(type));
 }