Check for readyState in video pixel tests

content/test/data/gpu/pixel_video_mp4.html

Index: content/test/data/gpu/pixel_video_mp4.html
diff --git a/content/test/data/gpu/pixel_video_mp4.html b/content/test/data/gpu/pixel_video_mp4.html
index 2a2bf900eb347758ce28ca10ad59607788d6e53d..0346bfe2fd7771734f1208d6b685e21b778fedf9 100644
--- a/content/test/data/gpu/pixel_video_mp4.html
+++ b/content/test/data/gpu/pixel_video_mp4.html
@@ -21,7 +21,11 @@ var video;
 function main()
 {
   video = document.getElementById("video");
-  video.addEventListener('canplaythrough', waitForFinish, true);
+  if (video.readyState >= 4) {
+    waitForFinish();
+  } else {
+    video.addEventListener('canplaythrough', waitForFinish, true);
+  }
 }
 
 function waitForFinish()