Define accelerated steps time function.

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 a6d19dabaaddd373032a3854330f6df91721fe52..1a75ac13ca65aca15bf9da4c36e026e7d1b1f5ba 100644
--- a/cc/blink/web_transform_animation_curve_impl.cc
+++ b/cc/blink/web_transform_animation_curve_impl.cc
@@ -40,6 +40,19 @@ void WebTransformAnimationCurveImpl::add(const WebTransformKeyframe& keyframe,
 }
 
 void WebTransformAnimationCurveImpl::add(const WebTransformKeyframe& keyframe,
+                                         int steps,
+                                         bool steps_at_start) {
+  const cc::TransformOperations& transform_operations =
+      static_cast<const WebTransformOperationsImpl&>(keyframe.value())
+          .AsTransformOperations();
+  curve_->AddKeyframe(cc::TransformKeyframe::Create(
+      keyframe.time(),
+      transform_operations,
+      cc::StepsTimingFunction::Create(steps, steps_at_start)
+          .PassAs<cc::TimingFunction>()));
+}
+
+void WebTransformAnimationCurveImpl::add(const WebTransformKeyframe& keyframe,
                                          double x1,
                                          double y1,
                                          double x2,