Bug 1404977 - Part 15 - Invalidate the device cache before re-enumerating devices when the cubeb backend does not support dynamic device collection invalidation. r=pehrsons

Also, clear the array that's been passed in before appending the new devices.

MozReview-Commit-ID: BTnwzyKBrb5

--HG--
extra : rebase_source : 23dbd11720804a30188389bc4408be4b40ad70b2

dom/media/webrtc/MediaEngineWebRTC.cpp

@@ -396,9 +396,11 @@ CubebDeviceEnumerator::EnumerateAudioInputDevices(nsTArray<RefPtr<AudioDeviceInf
   MutexAutoLock lock(mMutex);
 
   if (mDevices.IsEmpty() || mManualInvalidation) {
+    mDevices.Clear();
     CubebUtils::GetDeviceCollection(mDevices, CubebUtils::Input);
   }
 
+  aOutDevices.Clear();
   aOutDevices.AppendElements(mDevices);
 }