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

LayoutTests/media/track/track-remove-by-setting-innerHTML.html

Index: LayoutTests/media/track/track-remove-by-setting-innerHTML.html
diff --git a/LayoutTests/media/track/track-remove-by-setting-innerHTML.html b/LayoutTests/media/track/track-remove-by-setting-innerHTML.html
index a0df127b745e8b8203bd3a9c7f21570e1bfbc572..4ab20319eec3c5e0c010e14325e1c375763c6fe8 100644
--- a/LayoutTests/media/track/track-remove-by-setting-innerHTML.html
+++ b/LayoutTests/media/track/track-remove-by-setting-innerHTML.html
@@ -26,7 +26,7 @@
                 findMediaElement();
                 waitForEvent('error');
                 waitForEvent('seeked', seeked);
-                waitForEvent('canplaythrough', function()
+                waitForEventOnce('canplaythrough', function()
                 {
                     video.currentTime = 0.5;
                 });