Implement RTC[In/Out]boundRtpStreamStats.contentType.

Spec: https://henbos.github.io/webrtc-provisional-stats/#dom-rtcinboundrtpstreamstats-contenttype

This already exists as a goog-stat. This CL only plumbs the value to the
new stats collector.

Note: There is currently no distinction between the extension being
missing and it being present but the value being "unspecified". Until
https://crbug.com/webrtc/10529 is fixed, this metric is only exposed if
SCREENSHARE was present.

Bug: webrtc:10452
Change-Id: Ic8723f4d0efb43ab72a560e954676facd3b90659
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/131946
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Commit-Queue: Henrik Boström <hbos@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#27520}
diff --git a/pc/rtc_stats_collector.cc b/pc/rtc_stats_collector.cc
index df2f09c..7427356 100644
--- a/pc/rtc_stats_collector.cc
+++ b/pc/rtc_stats_collector.cc
@@ -19,6 +19,7 @@
 #include "api/candidate.h"
 #include "api/media_stream_interface.h"
 #include "api/peer_connection_interface.h"
+#include "api/video/video_content_type.h"
 #include "media/base/media_channel.h"
 #include "p2p/base/p2p_constants.h"
 #include "p2p/base/port.h"
@@ -266,6 +267,10 @@
   inbound_video->frames_decoded = video_receiver_info.frames_decoded;
   if (video_receiver_info.qp_sum)
     inbound_video->qp_sum = *video_receiver_info.qp_sum;
+  // TODO(https://crbug.com/webrtc/10529): When info's |content_info| is
+  // optional, support the "unspecified" value.
+  if (video_receiver_info.content_type == VideoContentType::SCREENSHARE)
+    inbound_video->content_type = RTCContentType::kScreenshare;
 }
 
 // Provides the media independent counters (both audio and video).
@@ -322,6 +327,10 @@
   outbound_video->total_encode_time =
       static_cast<double>(video_sender_info.total_encode_time_ms) /
       rtc::kNumMillisecsPerSec;
+  // TODO(https://crbug.com/webrtc/10529): When info's |content_info| is
+  // optional, support the "unspecified" value.
+  if (video_sender_info.content_type == VideoContentType::SCREENSHARE)
+    outbound_video->content_type = RTCContentType::kScreenshare;
 }
 
 void ProduceCertificateStatsFromSSLCertificateStats(