Define step timing function for the cc animation framework.

cc/blink/web_transform_animation_curve_impl.cc

Index: cc/blink/web_transform_animation_curve_impl.cc
diff --git a/cc/blink/web_transform_animation_curve_impl.cc b/cc/blink/web_transform_animation_curve_impl.cc
index 86f3602cecd560cdb10d4fe709d3a61ae117b697..80c1d1d02faaf9f7f0fae3ee0e10445b7e9c3c34 100644
--- a/cc/blink/web_transform_animation_curve_impl.cc
+++ b/cc/blink/web_transform_animation_curve_impl.cc
@@ -53,6 +53,17 @@ void WebTransformAnimationCurveImpl::add(const WebTransformKeyframe& keyframe,
       cc::CubicBezierTimingFunction::Create(x1, y1, x2, y2)));
 }
 
+void WebTransformAnimationCurveImpl::add(const WebTransformKeyframe& keyframe,
+                                         int steps,
+                                         float steps_start_offset) {
+  const cc::TransformOperations& transform_operations =
+      static_cast<const WebTransformOperationsImpl&>(keyframe.value())
+          .AsTransformOperations();
+  curve_->AddKeyframe(cc::TransformKeyframe::Create(
+      base::TimeDelta::FromSecondsD(keyframe.time()), transform_operations,
+      cc::StepsTimingFunction::Create(steps, steps_start_offset)));
+}
+
 void WebTransformAnimationCurveImpl::setTimingFunction(
     TimingFunctionType type) {
   curve_->SetTimingFunction(CreateTimingFunction(type));