Fix flakiness in webaudio/Oscillator/oscillator-late-start.html

third_party/WebKit/LayoutTests/webaudio/resources/late-start-testing.js

 function runLateStartTest(audit, context, node) {
 
   // Set up a dummy signal path to keep the audio context running and spend
   // processing time before calling start(0).
   var osc = context.createOscillator();
   var silent = context.createGain();
 
   osc.connect(silent);
   silent.connect(context.destination);
   silent.gain.setValueAtTime(0.0, 0);
   osc.start();
 
   node.connect(context.destination);
 
-  // Task: define |onstatechange| and start rendering.
+  // Task: schedule a suspend and start rendering.
   audit.defineTask('test-late-start', function (done) {
-
-    // Trigger playback at 0 second. The assumptions are:
-    //
-    // 1) The specified timing of start() call is already passed in terms of
-    // the context time. So the argument |0| will be clamped to the current
-    // context time.
-    // 2) The |onstatechange| event will be fired later than the 0 second
-    // context time.
-    //
+    // The node's start time will be clamped to the render quantum boundary
+    // >0.1 sec. Thus the rendered buffer will have non-zero frames.
     // See issue: crbug.com/462167
-    context.onstatechange = function () {
-      if (context.state === 'running') {
-        node.start(0);
-      }
-    };
+    context.suspend(0.1).then(() => {
+      node.start(0);
+      context.resume();
+    });
 
     // Start rendering and verify result: this verifies if 1) the rendered
     // buffer contains at least one non-zero value and 2) the non-zero value is
     // found later than the first output sample.
     context.startRendering().then(function (buffer) {
-
       var nonZeroValueIndex = -1;
       var channelData = buffer.getChannelData(0);
       for (var i = 0; i < channelData.length; i++) {
         if (channelData[i] !== 0) {
           nonZeroValueIndex = i;
           break;
         }
       }
 
-      if (nonZeroValueIndex === -1) {
-        testFailed('The rendered buffer was all zeros.');
-      } else if (nonZeroValueIndex === 0) {
-        testFailed('The first sample was non-zero value. It should be zero.');
-      } else {
-        testPassed('The rendered buffer contains non-zero values after the first sample.');
-      }
+      var success = Should('Non-zero value index', nonZeroValueIndex)
+          .notBeEqualTo(-1);

[Raymond Toy, 2017/02/13 22:13:01]

Nit: this is not a great message to print out. Don't have a really good
suggestion.

[hongchan, 2017/02/13 22:33:58]

Done.

+      success = Should('Non-zero value index', nonZeroValueIndex)
+          .notBeEqualTo(0) && success;

[Raymond Toy, 2017/02/13 22:13:02]

Maybe say 'First non-zero value found at index'. Or something.

[hongchan, 2017/02/13 22:33:58]

I changed it in a slightly different way.

+      Should('The rendered buffer', success)
+          .summarize('contains non-zero values after the first sample',
+                     'was all zeros or has non-zero first sample.');
 
       done();
     });
   });
 
   audit.defineTask('finish-test', function (done) {
     done();
     finishJSTest();
   });
 
   audit.runTasks(
     'test-late-start',
     'finish-test'
   );
 
-}
+}