Implement RTCOutboundRtpStreamStats.targetBitrate for video

Spec: https://w3c.github.io/webrtc-stats/#dom-rtcoutboundrtpstreamstats-targetbitrate

Bug: webrtc:13394
Change-Id: I4749b38088a24d1a775137d5fe2c65f96effd185
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/276380
Auto-Submit: Daniel.L (Byoungchan) Lee <daniel.l@hpcnt.com>
Commit-Queue: Henrik Boström <hbos@webrtc.org>
Reviewed-by: Henrik Boström <hbos@webrtc.org>
Reviewed-by: Ilya Nikolaevskiy <ilnik@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#38170}
diff --git a/pc/rtc_stats_integrationtest.cc b/pc/rtc_stats_integrationtest.cc
index 057bf0f..e49f173 100644
--- a/pc/rtc_stats_integrationtest.cc
+++ b/pc/rtc_stats_integrationtest.cc
@@ -956,6 +956,7 @@
         outbound_stream.header_bytes_sent);
     verifier.TestMemberIsNonNegative<uint64_t>(
         outbound_stream.retransmitted_bytes_sent);
+    verifier.TestMemberIsNonNegative<double>(outbound_stream.target_bitrate);
     if (outbound_stream.kind.is_defined() && *outbound_stream.kind == "video") {
       verifier.TestMemberIsDefined(outbound_stream.frames_encoded);
       verifier.TestMemberIsDefined(outbound_stream.key_frames_encoded);
@@ -990,7 +991,6 @@
       verifier.TestMemberIsNonNegative<uint32_t>(outbound_stream.frames_sent);
       verifier.TestMemberIsNonNegative<uint32_t>(
           outbound_stream.huge_frames_sent);
-      verifier.TestMemberIsUndefined(outbound_stream.target_bitrate);
       verifier.MarkMemberTested(outbound_stream.rid, true);
     } else {
       verifier.TestMemberIsUndefined(outbound_stream.frames_encoded);
@@ -1014,7 +1014,6 @@
       verifier.TestMemberIsUndefined(outbound_stream.frame_width);
       verifier.TestMemberIsUndefined(outbound_stream.frames_sent);
       verifier.TestMemberIsUndefined(outbound_stream.huge_frames_sent);
-      verifier.TestMemberIsNonNegative<double>(outbound_stream.target_bitrate);
     }
     return verifier.ExpectAllMembersSuccessfullyTested();
   }