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 71319e121d8c10ad3bf2f0c0a6b9dfd37c7bf165..25bd10e7ffd8415b2cc1967c5f4b2c46bdecd289 100644
--- a/cc/animation/timing_function.cc
+++ b/cc/animation/timing_function.cc
@@ -71,4 +71,38 @@ 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);
+}
+
+float StepsTimingFunction::Velocity(double x) const {
+  return 0.0f;
+}
+
 }  // namespace cc