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

LayoutTests/media/media-fragments/media-fragments.js

 
     var currentTest = null;
     var fragmentEndTime;
     var testData = 
     {
         // http://www.w3.org/2008/WebVideo/Fragments/TC/ua-test-cases
 
         TC0001 : { start: null, end: null, valid: false, description: "#t=,", fragment: "t=,", comment: "Syntax error, not allowed according to the ABNF. The media fragment is ignored."},
         TC0002 : { start: null, end: null, valid: false, description: "#t=a,a and a >= 0", fragment: "t=3,3", comment: "Invalid semantics: start must be smaller than end. The media fragment is ignored."},
         TC0003 : { start: null, end: null, valid: false, description: "#t=a,b and a > b", fragment: "t=7,3", comment: "Invalid semantics: the requested interval's start is beyond its end. The media fragment is ignored."},
@@ skipping 101 matching lines @@
     {
         video = document.createElement('video');
         video.setAttribute('id', 'vid'); 
         video.setAttribute('width', '320'); 
         video.setAttribute('height', '240'); 
         video.setAttribute('controls', ''); 
         var paragraph = document.createElement('p');
         paragraph.appendChild(video);
         document.body.appendChild(paragraph);
 
-        waitForEvent("canplaythrough", canplaythrough);
+        waitForEventOnce("canplaythrough", canplaythrough);
         waitForEvent("pause", pause);
 
         var fileName = location.href.split('/').pop();
         currentTest = fileName.substring(0, fileName.lastIndexOf("."));
 
         var info = testData[currentTest];
         consoleWrite("<br>Title: <b>" + currentTest + "</b>");
         consoleWrite("Fragment: '<i>" + info.fragment + "</i>'");
         consoleWrite("Comment: <i>" + info.comment + "</i>");
         url = findMediaFile("video", "../content/counting") + "#" + info.fragment;
         video.src = url;
     }