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 0e6fbbfa70eba489a6be885355ae7770eb399f88..c5aed82207c0f939ea1c03bf3fdabab8130fe597 100644
--- a/cc/animation/keyframed_animation_curve_unittest.cc
+++ b/cc/animation/keyframed_animation_curve_unittest.cc
@@ -427,6 +427,25 @@ 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(0.25f, curve->GetValue(0.25));

[ajuma, 2014/02/24 21:11:16]

0.25f

+  EXPECT_FLOAT_EQ(0.5f, curve->GetValue(0.5f));
+  EXPECT_FLOAT_EQ(0.75f, curve->GetValue(0.75));

[ajuma, 2014/02/24 21:11:16]

0.75f

+  EXPECT_FLOAT_EQ(1.f, curve->GetValue(1.f));

[ajuma, 2014/02/24 21:11:16]

It'd be good to also test values that don't land exactly on a step, e.g. 0.74f.

+}
+
 // Tests that animated bounds are computed as expected.
 TEST(KeyframedAnimationCurveTest, AnimatedBounds) {
   scoped_ptr<KeyframedTransformAnimationCurve> curve(