Disable AudioDeviceTest.StartPlayoutOnTwoInstances on iOS

webrtc/modules/audio_device/ios/audio_device_unittest_ios.cc

Index: webrtc/modules/audio_device/ios/audio_device_unittest_ios.cc
diff --git a/webrtc/modules/audio_device/ios/audio_device_unittest_ios.cc b/webrtc/modules/audio_device/ios/audio_device_unittest_ios.cc
index 76c50cbc791f3488d3490fd8eb610b2f33d93bfc..c2821815bab593548f1cde5fdb92a338b58fd3e6 100644
--- a/webrtc/modules/audio_device/ios/audio_device_unittest_ios.cc
+++ b/webrtc/modules/audio_device/ios/audio_device_unittest_ios.cc
@@ -620,7 +620,9 @@ TEST_F(AudioDeviceTest, StopPlayoutRequiresInitToRestart) {
 // last active instance shall deactivate the audio session. The test does not
 // explicitly verify correct audio session calls but instead focuses on
 // ensuring that audio starts for both ADMs.
-TEST_F(AudioDeviceTest, StartPlayoutOnTwoInstances) {
+
+// Failing when running on real iOS devices: bugs.webrtc.org/6889.
+TEST_F(AudioDeviceTest, DISABLED_StartPlayoutOnTwoInstances) {
   // Create and initialize a second/extra ADM instance. The default ADM is
   // created by the test harness.
   rtc::scoped_refptr<AudioDeviceModule> second_audio_device =