Define accelerated steps time function.

cc/animation/timing_function.cc

Index: cc/animation/timing_function.cc
diff --git a/cc/animation/timing_function.cc b/cc/animation/timing_function.cc
index bf11c20fe03a13f448f486ff600aef2005ea9d4c..5599b022696dd23b35b640c323fedd2a023fd890 100644
--- a/cc/animation/timing_function.cc
+++ b/cc/animation/timing_function.cc
@@ -67,4 +67,32 @@ scoped_ptr<TimingFunction> EaseInOutTimingFunction::Create() {
       0.42, 0.0, 0.58, 1).PassAs<TimingFunction>();
 }
 
+scoped_ptr<StepsTimingFunction> StepsTimingFunction::Create(
+    int steps, bool steps_at_start) {
+  return make_scoped_ptr(new StepsTimingFunction(steps, steps_at_start));
+}
+
+StepsTimingFunction::StepsTimingFunction(int steps,
+                                         bool steps_at_start)
+    : steps_(steps, steps_at_start) {}
+
+StepsTimingFunction::~StepsTimingFunction() {}
+
+float StepsTimingFunction::GetValue(double x) const {
+  return static_cast<float>(steps_.Solve(x));
+}
+
+scoped_ptr<AnimationCurve> StepsTimingFunction::Clone() const {
+  return make_scoped_ptr(
+      new StepsTimingFunction(*this)).PassAs<AnimationCurve>();
+}
+
+void StepsTimingFunction::Range(float* min, float* max) const {
+  double min_d = 0;
+  double max_d = 1;
+  steps_.Range(&min_d, &max_d);
+  *min = static_cast<float>(min_d);
+  *max = static_cast<float>(max_d);
+}
+
 }  // namespace cc