chromium: fix webrtc interaction with pulseaudio

The webrtc code suffered from a race condition when used
with Pulseaudio. This lead to audio input breaking every
couple of minutes during a webrtc session.

pkgs/applications/networking/browsers/chromium/common.nix

@@ -151,6 +151,8 @@ let
     ] ++ optionals (useVaapi) [
       # source: https://aur.archlinux.org/cgit/aur.git/tree/vaapi-fix.patch?h=chromium-vaapi
       ./patches/vaapi-fix.patch
+      # fix race condition in the interaction with pulseaudio
+      ./patches/webrtc-pulse.patch
     ];
 
     postPatch = ''

pkgs/applications/networking/browsers/chromium/patches/webrtc-pulse.patch

@@ -0,0 +1,61 @@
+From 704dc99bd05a94eb61202e6127df94ddfd571e85 Mon Sep 17 00:00:00 2001
+From: Dale Curtis <dalecurtis@chromium.org>
+Date: Mon, 02 Mar 2020 22:12:22 +0000
+Subject: [PATCH] Hold PulseAudio mainloop lock while querying input device info.
+
+a22cc23955cb3d58b7525c5103314226b3ce0137 moved this section out of
+UpdateNativeAudioHardwareInfo(), but forgot to bring the lock along.
+
+R=guidou
+
+Bug: 1043040
+Change-Id: I5b17a2cf0ad55d61c0811db1dae7045af4a91370
+Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2083814
+Commit-Queue: Dale Curtis <dalecurtis@chromium.org>
+Commit-Queue: Guido Urdaneta <guidou@chromium.org>
+Reviewed-by: Guido Urdaneta <guidou@chromium.org>
+Auto-Submit: Dale Curtis <dalecurtis@chromium.org>
+Cr-Commit-Position: refs/heads/master@{#746115}
+---
+
+diff --git a/media/audio/pulse/audio_manager_pulse.cc b/media/audio/pulse/audio_manager_pulse.cc
+index 90e9317..829846f 100644
+--- a/media/audio/pulse/audio_manager_pulse.cc
++++ b/media/audio/pulse/audio_manager_pulse.cc
+@@ -104,22 +104,27 @@
+ 
+ AudioParameters AudioManagerPulse::GetInputStreamParameters(
+     const std::string& device_id) {
+-  int user_buffer_size = GetUserBufferSize();
+-  int buffer_size =
+-      user_buffer_size ? user_buffer_size : kDefaultInputBufferSize;
+-
+   UpdateNativeAudioHardwareInfo();
+-  auto* operation = pa_context_get_source_info_by_name(
+-      input_context_, default_source_name_.c_str(), DefaultSourceInfoCallback,
+-      this);
+-  WaitForOperationCompletion(input_mainloop_, operation, input_context_);
++
++  {
++    AutoPulseLock auto_lock(input_mainloop_);
++    auto* operation = pa_context_get_source_info_by_name(
++        input_context_, default_source_name_.c_str(), DefaultSourceInfoCallback,
++        this);
++    WaitForOperationCompletion(input_mainloop_, operation, input_context_);
++  }
+ 
+   // We don't want to accidentally open a monitor device, so return invalid
+-  // parameters for those.
++  // parameters for those. Note: The value of |default_source_is_monitor_|
++  // depends on the the call to pa_context_get_source_info_by_name() above.
+   if (device_id == AudioDeviceDescription::kDefaultDeviceId &&
+       default_source_is_monitor_) {
+     return AudioParameters();
+   }
++
++  const int user_buffer_size = GetUserBufferSize();
++  const int buffer_size =
++      user_buffer_size ? user_buffer_size : kDefaultInputBufferSize;
+   return AudioParameters(AudioParameters::AUDIO_PCM_LOW_LATENCY,
+                          CHANNEL_LAYOUT_STEREO,
+                          native_input_sample_rate_ ? native_input_sample_rate_