Web Animations API: Implement step-middle and steps(x, middle) timing functions.

Source/core/animation/TimedItemCalculationsTest.cpp

Index: Source/core/animation/TimedItemCalculationsTest.cpp
diff --git a/Source/core/animation/TimedItemCalculationsTest.cpp b/Source/core/animation/TimedItemCalculationsTest.cpp
index 6e053cdde8f2193631cb54bd065815dd2360fbec..811ffdc66c63a57136648d686ad98459cac8109c 100644
--- a/Source/core/animation/TimedItemCalculationsTest.cpp
+++ b/Source/core/animation/TimedItemCalculationsTest.cpp
@@ -197,7 +197,7 @@ TEST(AnimationTimedItemCalculationsTest, TransformedTime)
     EXPECT_EQ(12, calculateTransformedTime(1, 20, 12, timing));
 
     // PlaybackDirectionForwards with timing function
-    timing.timingFunction = StepsTimingFunction::create(4, false /* stepAtStart */);
+    timing.timingFunction = StepsTimingFunction::create(4, StepsTimingFunction::StepAtEnd);
     EXPECT_EQ(10, calculateTransformedTime(0, 20, 12, timing));
     EXPECT_EQ(10, calculateTransformedTime(1, 20, 12, timing));
 
@@ -208,7 +208,7 @@ TEST(AnimationTimedItemCalculationsTest, TransformedTime)
     EXPECT_EQ(8, calculateTransformedTime(1, 20, 12, timing));
 
     // PlaybackDirectionReverse with timing function
-    timing.timingFunction = StepsTimingFunction::create(4, false /* stepAtStart */);
+    timing.timingFunction = StepsTimingFunction::create(4, StepsTimingFunction::StepAtEnd);
     EXPECT_EQ(5, calculateTransformedTime(0, 20, 12, timing));
     EXPECT_EQ(5, calculateTransformedTime(1, 20, 12, timing));