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

LayoutTests/animations/timing-functions.html

Index: LayoutTests/animations/timing-functions.html
diff --git a/LayoutTests/animations/timing-functions.html b/LayoutTests/animations/timing-functions.html
index bea1164741936c8fd407ded8fe39f72474f3a9de..d19422ec8e78571ab0100a25f6c3b91275fce500 100644
--- a/LayoutTests/animations/timing-functions.html
+++ b/LayoutTests/animations/timing-functions.html
@@ -43,6 +43,16 @@
     #box8 {
       -webkit-animation-timing-function: steps(3, end);
     }
+    /*
+     * The step-middle functions are invalid except through the Web Animations API
+     * and should behave like 'ease', unless step-middle has been added to the CSS specification.
+     */
+    #box9 {
+      -webkit-animation-timing-function: steps(3, middle);
+    }
+    #box10 {
+      -webkit-animation-timing-function: step-middle;
+    }
     
   </style>
   <script src="resources/animation-test-helpers.js" type="text/javascript" charset="utf-8"></script>
@@ -74,6 +84,12 @@
       [0.25, "box8", "left", 100, 5],
       [0.50, "box8", "left", 133, 5],
       [0.75, "box8", "left", 166, 5],
+      [0.25, "box9", "left", 141, 5],
+      [0.50, "box9", "left", 180, 5],
+      [0.75, "box9", "left", 196, 5],
+      [0.25, "box10", "left", 141, 5],
+      [0.50, "box10", "left", 180, 5],
+      [0.75, "box10", "left", 196, 5],
     ];
     
     runAnimationTest(expectedValues);
@@ -99,6 +115,10 @@ It takes 3 snapshots and expects each result to be within a specified range.
 </div>
 <div class="box" id="box8">
 </div>
+<div class="box" id="box9">
+</div>
+<div class="box" id="box10">
+</div>
 <div id="result">
 </div>
 </body>