Adjust a web platform test slightly to test that the parameter is a-r…

…ate.

bugzilla-url: https://bugzilla.mozilla.org/show_bug.cgi?id=1472550
gecko-commit: 5b8172ac07f62ad785c0d8df160696d3173bd9fe
gecko-integration-branch: autoland
gecko-reviewers: karlt

webaudio/the-audio-api/the-pannernode-interface/test-pannernode-automation.html

@@ -4,13 +4,18 @@
 <script src=/resources/testharness.js></script>
 <script src=/resources/testharnessreport.js></script>
 <script>
+
+// This value is purposefuly not aligned on a 128-block boundary so that we test
+// that the PannerNode position audioparam is a-rate.
+const POSITION_CHANGE_FRAME = 1111;
+
 promise_test(function(t) {
   var ac = new OfflineAudioContext(2, 2048, 44100);
   var panner = ac.createPanner();
   panner.positionX.value = -1;
   panner.positionY.value = -1;
   panner.positionZ.value = 1;
-  panner.positionX.setValueAtTime(1, 1024/ac.sampleRate);
+  panner.positionX.setValueAtTime(1, POSITION_CHANGE_FRAME/ac.sampleRate);
   var osc = ac.createOscillator();
   osc.connect(panner);
   panner.connect(ac.destination);
@@ -19,7 +24,7 @@
     var left = buffer.getChannelData(0);
     var right = buffer.getChannelData(1);
     for (var i = 0; i < 2048; ++i) {
-      if (i < 1024) {
+      if (i < POSITION_CHANGE_FRAME) {
         assert_true(Math.abs(left[i]) >= Math.abs(right[i]), "index " + i + " should be on the left");
       } else {
         assert_true(Math.abs(left[i]) < Math.abs(right[i]), "index " + i + " should be on the right");