Work around GC bug to fix flaky autoplay tests

LayoutTests/media/autoplay-with-preload-none.html

Index: LayoutTests/media/autoplay-with-preload-none.html
diff --git a/LayoutTests/media/autoplay-with-preload-none.html b/LayoutTests/media/autoplay-with-preload-none.html
index 732295c2d7610ba02686e6fb846c2a88dc977e2e..5128c9a310b550269fa2ccf066344df60cfaf0e2 100644
--- a/LayoutTests/media/autoplay-with-preload-none.html
+++ b/LayoutTests/media/autoplay-with-preload-none.html
@@ -10,6 +10,8 @@ function autoplay_test(tagName, src)
     async_test(function(t)
     {
         var e = document.createElement(tagName);
+        // add to body to prevent GC pending http://crbug.com/400659
+        document.body.appendChild(e);
         e.src = src;
         e.preload = "none";
         e.autoplay = true;