Make w3cwrapper.js's done() match the semantics in testharness.js

LayoutTests/media/W3C/w3cwrapper.js

 function getVideoURI(dummy) {
   var bool=function(any){return!(any=="no"||!any)};
   return "../../../content/test." + (bool(document.createElement("video").canPlayType('video/ogg; codecs="theora"')) ? "ogv" : "mp4");
 }
 
 function getAudioURI(dummy) {
   return "../../../content/test.wav";
 }
 
-function testStep(testFunction){
+function testStep(testFunction) {
   try {
     testFunction();
   } catch (e) {
     testFailed('Aborted with exception: ' + e.message);
   }
 }
 
+function testDone() {
+  // Match the semantics of testharness.js done(), where nothing that
+  // happens after that call has any effect on the test result.
+  if (!window.wasFinishJSTestCalled) {
+    finishJSTest();
+    assert_equals = assert_true = assert_false = function() { };
+  }
+}
+
 function test(testFunction) {
   description(document.title);
   testStep(testFunction);
 }
 
 function async_test(title, options) {
   window.jsTestIsAsync = true;
   description(title);
   return {
     step: testStep,
-    done: finishJSTest
+    done: testDone
   }
 }
 
 document.write("<p id=description></p><div id=console></div>");
 document.write("<script src='../../../../resources/js-test.js'></" + "script>");
 
 assert_equals = function(a, b) { shouldBe('"' + a + '"', '"' + b + '"'); }
 assert_true = function(a) { shouldBeTrue("" + a); }
 assert_false = function(a) { shouldBeFalse("" + a); }
 
 if (window.testRunner)
   testRunner.dumpAsText();