bug 1208318 modify test to avoid assuming different clocks are synchronized r=padenot

--HG--
extra : rebase_source : 31ecead7358bdb7b511d5efd802f479af46aef42

dom/media/webaudio/test/test_scriptProcessorNode_playbackTime1.html

@@ -10,31 +10,35 @@
 <script class="testbody" type="text/javascript">
 
 SimpleTest.waitForExplicitFinish();
-SimpleTest.requestFlakyTimeout("This test needs to wait until after the AudioContext's timer has started.");
-addLoadEvent(
+SimpleTest.requestFlakyTimeout(
+  "This test needs to wait until AudioDestinationNode has started has " +
+  "accumulated some 'extra' time.");
+
+var context = new AudioContext();
+const delay = 0.1;
+
+setTimeout(
   function() {
-    const delay = 0.1;
-    var context = new AudioContext();
-    SimpleTest.executeSoon( // to ensure that AudioContext has started
-      function() {
-        setTimeout( // wait for |delay|
-          function() {
-            var sp = context.createScriptProcessor(256);
-            sp.connect(context.destination);
-            sp.onaudioprocess =
-              function(e) {
-                var minimum =
-                  (delay + e.inputBuffer.length/context.sampleRate) *
-                  (1.0 - 1.0/Math.pow(2.0,52.0)); // double precision
-                ok(e.playbackTime >= minimum,
-                   "playbackTime " + e.playbackTime +
-                   " beyond expected minimum " + minimum);
-                sp.onaudioprocess = null;
-                SimpleTest.finish();
-              };
-          }, 1000 * delay);
-      });
-  });
+    const processorBufferLength = 256;
+    // |currentTime| may include double precision floating point
+    // rounding errors, so round to nearest integer sample to ignore these.
+    var minimumPlaybackSample =
+      Math.round(context.currentTime * context.sampleRate) +
+      processorBufferLength;
+    var sp = context.createScriptProcessor(processorBufferLength);
+    sp.connect(context.destination);
+    sp.onaudioprocess =
+      function(e) {
+        is(e.inputBuffer.length, processorBufferLength,
+           "expected buffer length");
+        var playbackSample = Math.round(e.playbackTime * context.sampleRate)
+        ok(playbackSample >= minimumPlaybackSample,
+           "playbackSample " + playbackSample +
+           " beyond expected minimum " + minimumPlaybackSample);
+        sp.onaudioprocess = null;
+        SimpleTest.finish();
+      };
+  }, 1000 * delay);
 
 </script>
 </pre>