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 e88c7d11c83a4ac74e2e72d85d4922cb34b8dca9..6d96c05416f6f882bf71fd31850560b396f91638 100644
--- a/Source/core/animation/TimedItemCalculationsTest.cpp
+++ b/Source/core/animation/TimedItemCalculationsTest.cpp
@@ -184,7 +184,7 @@ 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));
 
@@ -195,7 +195,7 @@ 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));