Enable DSCP by default.

DSCP is controlled by the spec-compliant API
RTCRtpEncodingParameters.networkPriority[1]. It already has a default
value that is the same as when DSCP is disabled.
- If you want non-default DSCP default values, you need to set
  networkPriority and shouldn't need to set a non-standard googDscp flag
  for it to have an effect.
- If you want the default DSCP value, you wouldn't change
  networkPriority and so you don't care if enable_dscp is true... you'll
  get the default regardless.

Drive-by: This CL also adds crbug references to other goog flags.

[1] https://w3c.github.io/webrtc-priority/#dom-rtcrtpencodingparameters-networkpriority

Bug: chromium:1315574
Change-Id: I15a0470fa04f55e2534cee0d240eeb03446c2de6
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/258940
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Commit-Queue: Henrik Boström <hbos@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#36550}

api/peer_connection_interface.h

@@ -428,8 +428,8 @@ class RTC_EXPORT PeerConnectionInterface : public rtc::RefCountInterface {
     //////////////////////////////////////////////////////////////////////////
 
     // If set to true, don't gather IPv6 ICE candidates.
-    // TODO(deadbeef): Remove this? IPv6 support has long stopped being
-    // experimental
+    // TODO(https://crbug.com/1315576): Remove the ability to set it in Chromium
+    // and delete this flag.
     bool disable_ipv6 = false;
 
     // If set to true, don't gather IPv6 ICE candidates on Wi-Fi.

media/base/media_channel.h

@@ -137,6 +137,8 @@ struct VideoOptions {
   // Force screencast to use a minimum bitrate. This flag comes from
   // the PeerConnection constraint 'googScreencastMinBitrate'. It is
   // copied to the encoder config by WebRtcVideoChannel.
+  // TODO(https://crbug.com/1315155): Remove the ability to set it in Chromium
+  // and delete this flag (it should default to 100 kbps).
   absl::optional<int> screencast_min_bitrate_kbps;
   // Set by screencast sources. Implies selection of encoding settings
   // suitable for screencast. Most likely not the right way to do

media/base/media_config.h

@@ -18,12 +18,16 @@ namespace cricket {
 struct MediaConfig {
   // Set DSCP value on packets. This flag comes from the
   // PeerConnection constraint 'googDscp'.
-  bool enable_dscp = false;
+  // TODO(https://crbug.com/1315574): Remove the ability to set it in Chromium
+  // and delete this flag.
+  bool enable_dscp = true;
 
   // Video-specific config.
   struct Video {
     // Enable WebRTC CPU Overuse Detection. This flag comes from the
     // PeerConnection constraint 'googCpuOveruseDetection'.
+    // TODO(https://crbug.com/1315569): Remove the ability to set it in Chromium
+    // and delete this flag.
     bool enable_cpu_adaptation = true;
 
     // Enable WebRTC suspension of video. No video frames will be sent
@@ -31,6 +35,8 @@ struct MediaConfig {
     // flag comes from the PeerConnection constraint
     // 'googSuspendBelowMinBitrate', and WebRtcVideoChannel copies it
     // to VideoSendStream::Config::suspend_below_min_bitrate.
+    // TODO(https://crbug.com/1315564): Remove the ability to set it in Chromium
+    // and delete this flag.
     bool suspend_below_min_bitrate = false;
 
     // Enable buffering and playout timing smoothing of decoded frames.

pc/peer_connection_interface_unittest.cc

@@ -3692,7 +3692,7 @@ TEST_F(PeerConnectionMediaConfigTest, TestDefaults) {
 
   const cricket::MediaConfig& media_config = TestCreatePeerConnection(config);
 
-  EXPECT_FALSE(media_config.enable_dscp);
+  EXPECT_TRUE(media_config.enable_dscp);
   EXPECT_TRUE(media_config.video.enable_cpu_adaptation);
   EXPECT_TRUE(media_config.video.enable_prerenderer_smoothing);
   EXPECT_FALSE(media_config.video.suspend_below_min_bitrate);