Fix flaky WebAudio layout tests

third_party/WebKit/LayoutTests/webaudio/audiochannelmerger-disconnect.html

Index: third_party/WebKit/LayoutTests/webaudio/audiochannelmerger-disconnect.html
diff --git a/third_party/WebKit/LayoutTests/webaudio/audiochannelmerger-disconnect.html b/third_party/WebKit/LayoutTests/webaudio/audiochannelmerger-disconnect.html
index c100b8f4d629e8f188ba8484cd97c2aba019e9a7..c9724cb8d0246e5508414de4332ba946fa398062 100644
--- a/third_party/WebKit/LayoutTests/webaudio/audiochannelmerger-disconnect.html
+++ b/third_party/WebKit/LayoutTests/webaudio/audiochannelmerger-disconnect.html
@@ -12,29 +12,24 @@
     description('Test ChannelMergerNode behavior on dynamic input change.');
     window.jsTestIsAsync = true;
 
-    var sampleRate = 44100;
     var numberOfChannels = 2;
-
-    // The test needs the long render length (20 seconds) to capture the
-    // disconnection which happens after starting the rendering. 
-    var renderLength = sampleRate * 20;
+    var sampleRate = 44100;
+    var renderLength = 2 * sampleRate;
 
     var audit = Audit.createTaskRunner();
 
     // Task: Check if the merger outputs a silent channel when an input is
     // disconnected.
     audit.defineTask('silent-disconnect', function (done) {
-      var context = new OfflineAudioContext(
-        numberOfChannels, renderLength, sampleRate
-      );
+      var context = new OfflineAudioContext(numberOfChannels, renderLength, sampleRate);
       var merger = context.createChannelMerger();
       var source1 = context.createBufferSource();
       var source2 = context.createBufferSource();
 
-      // Create and assign a mono testing buffer.
-      var bufferDCOffset = createTestingAudioBuffer(context, 1, renderLength);
-      source1.buffer = bufferDCOffset;
-      source2.buffer = bufferDCOffset;
+      // Create and assign a constant buffer.
+      var bufferDCOffset = createConstantBuffer(context, 1, 1);
+      source1.buffer = source2.buffer = bufferDCOffset;
+      source1.loop = source2.loop = true;
 
       // Connect the output of source into the 4th input of merger. The merger
       // should produce 6 channel output.
@@ -43,23 +38,20 @@
       merger.connect(context.destination);
       source1.start();
       source2.start();
-
-      // When the rendering begins, disconnect |source2| as soon as possible.
-      context.onstatechange = function () {
-        if (context.state === 'running')
-          source2.disconnect();
-      };
+      
+      // Schedule the disconnection of |source2| at 1 second.

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

We could make this test much faster if we didn't render so much.  Maybe just run
the test for a 1/4 second and disconnect at 1/8?

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

I thought you'd ask! I will reduce the render length of all tests to quarter
second.

[Raymond Toy, 2015/12/02 19:37:50]

Seems to me that you did 1/2 sec for the tests.  That's ok though.

+      context.suspend(1.0).then(function () {
+        source2.disconnect();
+        context.resume();
+      });
 
       context.startRendering().then(function (buffer) {
-
         // The entire first channel of the output should be 1.
         Should('Channel #0', buffer.getChannelData(0)).beConstantValueOf(1);
 
         // The second channel should contain 1, and 0 after the disconnection.

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

Now that we know exactly when the disconnect happens, we should check that the
second channel switches to 0 at exactly the right place.

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

Done.

         Should('Channel #1', buffer.getChannelData(1)).containValues([1, 0]);
-
-        done();
-      });
+      }).then(done);
     });
 
     audit.defineTask('finish', function (done) {
@@ -67,10 +59,7 @@
       done();
     });
 
-    audit.runTasks(
-      'silent-disconnect',
-      'finish'
-    );
+    audit.runTasks();
 
     successfullyParsed = true;
   </script>