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

LayoutTests/animations/animations-parsing.html

Index: LayoutTests/animations/animations-parsing.html
diff --git a/LayoutTests/animations/animations-parsing.html b/LayoutTests/animations/animations-parsing.html
index ba993985bb38da673363b24e0a82d5907ba03b29..77d0b32ce3c8c149afeb81b6bd0ffce09ac9038d 100644
--- a/LayoutTests/animations/animations-parsing.html
+++ b/LayoutTests/animations/animations-parsing.html
@@ -402,6 +402,18 @@ shouldBe("computedStyle.animationTimingFunction", "'ease'");
 shouldBe("style.webkitAnimationTimingFunction", "''");
 shouldBe("computedStyle.webkitAnimationTimingFunction", "'ease'");
 
+style.animationTimingFunction = "step-middle";
+shouldBe("style.animationTimingFunction", "'step-middle'");
+shouldBe("computedStyle.animationTimingFunction", "'ease'");
+shouldBe("style.webkitAnimationTimingFunction", "'step-middle'");
+shouldBe("computedStyle.webkitAnimationTimingFunction", "'ease'");
+
+style.animationTimingFunction = "steps(5, middle)";
+shouldBe("style.animationTimingFunction", "'steps(5, middle)'");
+shouldBe("computedStyle.animationTimingFunction", "'ease'");
+shouldBe("style.webkitAnimationTimingFunction", "'steps(5, middle)'");
+shouldBe("computedStyle.webkitAnimationTimingFunction", "'ease'");
+
 debug("Valid animation-delay values.");
 // Initial test.
 shouldBe("computedStyle.animationDelay", "'0s'");