Fix LayoutTests that assume canplay, playing, and canplaythrough will only fire once.

LayoutTests/media/audio-garbage-collect.html

Index: LayoutTests/media/audio-garbage-collect.html
diff --git a/LayoutTests/media/audio-garbage-collect.html b/LayoutTests/media/audio-garbage-collect.html
index 8b55931ed00f9dc54565576d52fa6e47f12d18b5..d7184cf106bfd60c34bdbd299a4da117cf797ed8 100644
--- a/LayoutTests/media/audio-garbage-collect.html
+++ b/LayoutTests/media/audio-garbage-collect.html
@@ -50,10 +50,11 @@ function start() {
                 finish();
         }
     });
-    a.addEventListener('canplaythrough', function() {
+
+    waitForEvent('canplaythrough', function() {
         a.currentTime = a.duration - 0.35;
         a.play();
-    });
+    }, false, true, a, true);
 }
 
 start();