Fix animations not starting on detached elements

LayoutTests/animations/insert-style-dependent-animation.html

Index: LayoutTests/animations/insert-style-dependent-animation.html
diff --git a/LayoutTests/animations/composited-animation-style-update.html b/LayoutTests/animations/insert-style-dependent-animation.html
similarity index 77%
copy from LayoutTests/animations/composited-animation-style-update.html
copy to LayoutTests/animations/insert-style-dependent-animation.html
index 25f7a923af013aeecb4e8b7b9c1ee1015db12239..65ff334bbc344653d11923347dc389cdc72fa29e 100644
--- a/LayoutTests/animations/composited-animation-style-update.html
+++ b/LayoutTests/animations/insert-style-dependent-animation.html
@@ -4,23 +4,18 @@ div {
     position: absolute;
     width: 100px;
     height: 100px;
+    font-size: 50px;
 }
 
 #expectation {
-    font-size: 50px;
     background: red;
     transform: translate(1em, 1em);
 }
-
-#target {
-    font-size: 1px;
-    background: green;
-}
 </style>
 <div id="expectation"></div>
-<div id="target"></div>
 <script>
-target.style.fontSize = "50px";
+var target = document.createElement('div');
+target.style.background = 'green';
 target.animate([
   {transform: "translate(1em, 1em)"},
   {transform: "translate(1em, 1em)"},
@@ -28,4 +23,5 @@ target.animate([
   duration: 1000,
   iterations: Infinity,
 });
+document.body.appendChild(target);
 </script>