Define accelerated steps time function.

cc/animation/keyframed_animation_curve_unittest.cc

Index: cc/animation/keyframed_animation_curve_unittest.cc
diff --git a/cc/animation/keyframed_animation_curve_unittest.cc b/cc/animation/keyframed_animation_curve_unittest.cc
index eceba6fc9e550b3278c6ba7d3fbc871011272de2..572346af06d8ee012589bc46b6e78e98eadd3acd 100644
--- a/cc/animation/keyframed_animation_curve_unittest.cc
+++ b/cc/animation/keyframed_animation_curve_unittest.cc
@@ -427,6 +427,28 @@ TEST(KeyframedAnimationCurveTest, CubicBezierTimingFunction) {
   EXPECT_FLOAT_EQ(1.f, curve->GetValue(1.f));
 }
 
+// Tests that a steps timing function works as expected.
+TEST(KeyframedAnimationCurveTest, StepsTimingFunction) {
+  scoped_ptr<KeyframedFloatAnimationCurve> curve(
+      KeyframedFloatAnimationCurve::Create());
+  curve->AddKeyframe(FloatKeyframe::Create(
+      0.0,
+      0.f,
+      StepsTimingFunction::Create(36, false).PassAs<TimingFunction>()));
+  curve->AddKeyframe(
+      FloatKeyframe::Create(1.0, 1.f, scoped_ptr<TimingFunction>()));
+
+  EXPECT_FLOAT_EQ(0.f, curve->GetValue(0.f));
+  EXPECT_FLOAT_EQ(7.0 / 36.0, curve->GetValue(0.20f));
+  EXPECT_FLOAT_EQ(0.25f, curve->GetValue(0.25f));
+  EXPECT_FLOAT_EQ(10.0 / 36.0, curve->GetValue(0.30f));
+  EXPECT_FLOAT_EQ(0.5f, curve->GetValue(0.5f));
+  EXPECT_FLOAT_EQ(21.0 / 36.0, curve->GetValue(0.60f));
+  EXPECT_FLOAT_EQ(0.75f, curve->GetValue(0.75f));
+  EXPECT_FLOAT_EQ(32.0 / 36.0, curve->GetValue(0.90f));
+  EXPECT_FLOAT_EQ(1.f, curve->GetValue(1.f));
+}
+
 // Tests that animated bounds are computed as expected.
 TEST(KeyframedAnimationCurveTest, AnimatedBounds) {
   scoped_ptr<KeyframedTransformAnimationCurve> curve(