Web Animations: Support iterator protocol in property indexed keyframe values

third_party/WebKit/LayoutTests/animations/element-animate-iterable-keyframes.html

Index: third_party/WebKit/LayoutTests/animations/element-animate-iterable-keyframes.html
diff --git a/third_party/WebKit/LayoutTests/animations/element-animate-iterable-keyframes.html b/third_party/WebKit/LayoutTests/animations/element-animate-iterable-keyframes.html
index 09d9a279f08ac8745af7b134c9f87fcaff2d4410..f6df994f99eb5e73566cb918ff208078a2cbe019 100644
--- a/third_party/WebKit/LayoutTests/animations/element-animate-iterable-keyframes.html
+++ b/third_party/WebKit/LayoutTests/animations/element-animate-iterable-keyframes.html
@@ -44,6 +44,26 @@ test(() => {
 }, 'Custom iterator with basic keyframes.');
 
 test(() => {
+  assertAnimationEffect({
+    keyframes: {
+      left: createIterable([
+        {done: false, value: '100px'},
+        {done: false, value: '300px'},
+        {done: false, value: '200px'},
+        {done: true},
+      ]),
+    },
+    expect: [
+      {at: 0, is: {left: '100px'}},
+      {at: 0.25, is: {left: '200px'}},
+      {at: 0.5, is: {left: '300px'}},
+      {at: 0.75, is: {left: '250px'}},
+      {at: 1, is: {left: '200px'}},
+    ],
+  });
+}, 'Custom iterator with property indexed keyframes.');
+
+test(() => {
   var keyframes = createIterable([
     {done: false, value: {left: '100px'}},
     {done: false, value: {left: '300px'}},