Fix flaky WebAudio layout tests

third_party/WebKit/LayoutTests/webaudio/audionode-disconnect-audioparam.html

Index: third_party/WebKit/LayoutTests/webaudio/audionode-disconnect-audioparam.html
diff --git a/third_party/WebKit/LayoutTests/webaudio/audionode-disconnect-audioparam.html b/third_party/WebKit/LayoutTests/webaudio/audionode-disconnect-audioparam.html
index 3c9f1fb4d523d31e29f039d0a096a90fa9c2ffb7..84d1565f37ac1cf689ea4666bb1084f754ab1138 100644
--- a/third_party/WebKit/LayoutTests/webaudio/audionode-disconnect-audioparam.html
+++ b/third_party/WebKit/LayoutTests/webaudio/audionode-disconnect-audioparam.html
@@ -12,12 +12,10 @@
     description('Test disconnect() method on AudioParam destination.');
     window.jsTestIsAsync = true;
 
-    var audit = Audit.createTaskRunner();
+    var sampleRate = 44100;
+    var renderLength = 2 * sampleRate;
 
-    // The long render length (20 seconds) test 1 and 2 is to make sure the 
-    // |onstatechange| event gets fired to start the source, which can take
-    // quite a bit of time.
-    var testDuration = 20;
+    var audit = Audit.createTaskRunner();
 
     // Task 1: test disconnect(AudioParam) method.
     audit.defineTask('disconnect(AudioParam)', function (done) {
@@ -25,14 +23,16 @@
       // Creates a buffer source with value [1] and then connect it to two gain
       // nodes in series. The output of the buffer source is lowered by half 
       // (* 0.5) and then connected to two |.gain| AudioParams in each gain node.
+      // 
       //  (1) bufferSource => gain1 => gain2
       //  (2) bufferSource => half => gain1.gain
       //  (3) half => gain2.gain
+      //  
       // This graph should produce the output of 2.25 (= 1 * 1.5 * 1.5). After
       // disconnecting (3), it should produce 1.5.
-      var context = new OfflineAudioContext(1, 44100 * testDuration, 44100);
+      var context = new OfflineAudioContext(1, renderLength, sampleRate);
       var source = context.createBufferSource();
-      var buffer1ch = createTestingAudioBuffer(context, 1, 128);
+      var buffer1ch = createTestingAudioBuffer(context, 1, 1);
       var half = context.createGain();
       var gain1 = context.createGain();
       var gain2 = context.createGain();
@@ -54,26 +54,14 @@
       
       source.start();
 
-      // Disconnects after the rendering starts.
-      // 
-      // FIXME: Although this guarantees that the disconnection happens after 
-      // the rendering starts, still the actual disconnection might happen after
-      // oncomplete event fired.
-      // 
-      // The 10ms delay is 1/1000 of the total render length (10,000ms). Because 
-      // OfflineAudioContext runs faster than real time, the disconnection might
-      // happen after the rendering finishes. Then lower the delay and increase 
-      // the render length to avoid the test failure.
-      context.onstatechange = function () {
-        if (context.state === 'running')
-          half.disconnect(gain2.gain);
-      };
+      // Schedule the disconnection at 1.0 second.

[Raymond Toy, 2015/12/01 22:14:37]

Can we run the test for a much shorter duration?  Say 1/4 sec total with
disconnect at 1/8 sec?

Does it matter if the disconnect isn't on a rendering quantum?

Same issue for the tasks below.

[hongchan, 2015/12/02 18:58:31]

Done.

+      context.suspend(1.0).then(function () {
+        half.disconnect(gain2.gain);
+        context.resume();
+      });
 
       context.startRendering().then(function (buffer) {
-
-        // Note that this test depends on the disconnection below to happen
-        // sometime during rendering.
-
+        
         // Expected values are: 1 * 1.5 * 1.5 -> 1 * 1.5 = [2.25, 1.5]

[Raymond Toy, 2015/12/01 22:14:37]

We should probably check the values change at exactly the correct time since we
now know exactly when the disconnect happens.

Same issue for the other task below.

[hongchan, 2015/12/02 18:58:32]

Done.

         Should('Channel #0', buffer.getChannelData(0)).containValues([2.25, 1.5]);
         
@@ -87,13 +75,15 @@
       // make a serial connection through gain1 and gain 2. The make the buffer
       // source half with a gain node and connect it to a 2-output splitter.
       // Connect each output to 2 gain AudioParams respectively.
+      // 
       //    (1) bufferSource => gain1 => gain2
       //    (2) bufferSource => half => splitter(2)
       //    (3) splitter#0 => gain1.gain
       //    (4) splitter#1 => gain2.gain
+      //    
       // This graph should produce 3 (= 1 * 1.5 * 2) and 6 (= 2 * 1.5 * 2) for 
       // each channel. After disconnecting (4), it should output 1.5 and 3.
-      var context = new OfflineAudioContext(2, 44100 * testDuration, 44100);
+      var context = new OfflineAudioContext(2, renderLength, sampleRate);
       var source = context.createBufferSource();
       var buffer2ch = createTestingAudioBuffer(context, 2, 128);
       var splitter = context.createChannelSplitter(2);
@@ -123,12 +113,11 @@
 
       source.start();
 
-      // Disconnect after the rendering starts. See the comment in the previous
-      // test task.
-      context.onstatechange = function () {
-        if (context.state === 'running')
-          splitter.disconnect(gain2.gain, 1);
-      };
+      // Schedule the disconnect at 1 second.
+      context.suspend(1.0).then(function () {
+        splitter.disconnect(gain2.gain, 1);
+        context.resume();
+      });
 
       context.startRendering().then(function (buffer) {