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

LayoutTests/media/event-attributes.html

Index: LayoutTests/media/event-attributes.html
diff --git a/LayoutTests/media/event-attributes.html b/LayoutTests/media/event-attributes.html
index dfd4f97493d1fd2c8f0f91e2497c20d6493665fb..a7e15f35f2bd646d1c2bc511f8662dc672b4faed 100644
--- a/LayoutTests/media/event-attributes.html
+++ b/LayoutTests/media/event-attributes.html
@@ -18,9 +18,11 @@
                 switch (event.type)
                 {
                     case "canplaythrough":
+                        if (playingCount > 0)
+                            return;
                         testExpected('progressEventCount', 1, '>=');
                         consoleWrite("<br>*** starting playback");
-                        run("video.play()"); 
+                        run("video.play()");
                         break;
                     case "playing":
                         if (++playingCount == 1) {