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

LayoutTests/media/W3C/w3cwrapper.js

Index: LayoutTests/media/W3C/w3cwrapper.js
diff --git a/LayoutTests/media/W3C/w3cwrapper.js b/LayoutTests/media/W3C/w3cwrapper.js
index 203c74f077329ee34a1fac1c23fcef200deb28d3..c84c66b1dc0bf57da50a7b9d7903b16e53a7a5e9 100644
--- a/LayoutTests/media/W3C/w3cwrapper.js
+++ b/LayoutTests/media/W3C/w3cwrapper.js
@@ -7,7 +7,7 @@ function getAudioURI(dummy) {
   return "../../../content/test.wav";
 }
 
-function testStep(testFunction){
+function testStep(testFunction) {
   try {
     testFunction();
   } catch (e) {
@@ -15,6 +15,15 @@ function testStep(testFunction){
   }
 }
 
+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);
@@ -25,7 +34,7 @@ function async_test(title, options) {
   description(title);
   return {
     step: testStep,
-    done: finishJSTest
+    done: testDone
   }
 }