Define accelerated steps time function.

cc/blink/web_filter_animation_curve_impl.cc

Index: cc/blink/web_filter_animation_curve_impl.cc
diff --git a/cc/blink/web_filter_animation_curve_impl.cc b/cc/blink/web_filter_animation_curve_impl.cc
index cfbe191cb23345c495352737f354c8e3eb0dbd46..002a62a8e13bc5e3b008fc129260939d42c76c42 100644
--- a/cc/blink/web_filter_animation_curve_impl.cc
+++ b/cc/blink/web_filter_animation_curve_impl.cc
@@ -36,6 +36,19 @@ void WebFilterAnimationCurveImpl::add(const WebFilterKeyframe& keyframe,
 }
 
 void WebFilterAnimationCurveImpl::add(const WebFilterKeyframe& keyframe,
+                                      int steps,
+                                      bool steps_at_start) {
+  const cc::FilterOperations& filter_operations =
+      static_cast<const WebFilterOperationsImpl&>(keyframe.value())
+          .AsFilterOperations();
+  curve_->AddKeyframe(cc::FilterKeyframe::Create(
+      keyframe.time(),
+      filter_operations,
+      cc::StepsTimingFunction::Create(steps, steps_at_start)
+          .PassAs<cc::TimingFunction>()));
+}
+
+void WebFilterAnimationCurveImpl::add(const WebFilterKeyframe& keyframe,
                                       double x1,
                                       double y1,
                                       double x2,