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..958cb1206b07a46a45525e48e442f8cc2eb304f6 100644
--- a/third_party/WebKit/LayoutTests/webaudio/audiochannelmerger-disconnect.html
+++ b/third_party/WebKit/LayoutTests/webaudio/audiochannelmerger-disconnect.html
@@ -12,29 +12,27 @@
     description('Test ChannelMergerNode behavior on dynamic input change.');
     window.jsTestIsAsync = true;
 
-    var sampleRate = 44100;
-    var numberOfChannels = 2;
+    var renderQuantum = 128;
 
-    // The test needs the long render length (20 seconds) to capture the
-    // disconnection which happens after starting the rendering. 
-    var renderLength = sampleRate * 20;
+    var numberOfChannels = 2;
+    var sampleRate = 44100;
+    var renderDuration = 0.5;
+    var disconnectTime = 0.5 * renderDuration;
 
     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, renderDuration * sampleRate, 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.
@@ -44,22 +42,31 @@
       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 the half of render duration.
+      context.suspend(disconnectTime).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);
 
+        // Calculate the first zero index in the second channel.
+        var channel1 = buffer.getChannelData(1);
+        var disconnectIndex = disconnectTime * sampleRate; 
+        disconnectIndex -= (disconnectIndex) % renderQuantum;
+        var firstZeroIndex = channel1.findIndex(function (element, index) {
+          if (element === 0)
+            return index;
+        });
+
         // The second channel should contain 1, and 0 after the disconnection.
-        Should('Channel #1', buffer.getChannelData(1)).containValues([1, 0]);
+        Should('Channel #1', channel1).containValues([1, 0]);
+        Should('The index of first zero in the channel #1', firstZeroIndex)
+          .beEqualTo(disconnectIndex);
 
-        done();
-      });
+      }).then(done);
     });
 
     audit.defineTask('finish', function (done) {
@@ -67,10 +74,7 @@
       done();
     });
 
-    audit.runTasks(
-      'silent-disconnect',
-      'finish'
-    );
+    audit.runTasks();
 
     successfullyParsed = true;
   </script>