Fix flaky WebAudio layout tests

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.
-  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.
-    //
-    // See issue: crbug.com/462167
-    context.onstatechange = function () {
-      if (context.state === 'running') {
-        node.start(0);
-      }
-    };
-
-    // 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.');
-      }
-
-      done();
-    });
-  });
-
-  audit.defineTask('finish-test', function (done) {
-    done();
-    finishJSTest();
-  });
-
-  audit.runTasks(
-    'test-late-start',
-    'finish-test'
-  );
-
-}