Log last received RTP timestamp when requesting a PLI due to timeout

which helps finding the associated packets in Wireshark dumps

BUG=None

Change-Id: I216b3e87606b914781c3a2ed61a0118dcd7c1ec2
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/308822
Reviewed-by: Ilya Nikolaevskiy <ilnik@webrtc.org>
Reviewed-by: Henrik Boström <hbos@webrtc.org>
Commit-Queue: Philipp Hancke <phancke@microsoft.com>
Cr-Commit-Position: refs/heads/main@{#40397}
diff --git a/video/rtp_video_stream_receiver2.cc b/video/rtp_video_stream_receiver2.cc
index a01e60f..7634764 100644
--- a/video/rtp_video_stream_receiver2.cc
+++ b/video/rtp_video_stream_receiver2.cc
@@ -1039,6 +1039,12 @@
   return absl::nullopt;
 }
 
+absl::optional<uint32_t>
+RtpVideoStreamReceiver2::LastReceivedFrameRtpTimestamp() const {
+  RTC_DCHECK_RUN_ON(&packet_sequence_checker_);
+  return last_received_rtp_timestamp_;
+}
+
 absl::optional<int64_t> RtpVideoStreamReceiver2::LastReceivedKeyframePacketMs()
     const {
   RTC_DCHECK_RUN_ON(&packet_sequence_checker_);
diff --git a/video/rtp_video_stream_receiver2.h b/video/rtp_video_stream_receiver2.h
index f9ed339..0178355 100644
--- a/video/rtp_video_stream_receiver2.h
+++ b/video/rtp_video_stream_receiver2.h
@@ -204,6 +204,7 @@
   void SetProtectionPayloadTypes(int red_payload_type, int ulpfec_payload_type);
 
   absl::optional<int64_t> LastReceivedPacketMs() const;
+  absl::optional<uint32_t> LastReceivedFrameRtpTimestamp() const;
   absl::optional<int64_t> LastReceivedKeyframePacketMs() const;
 
  private:
diff --git a/video/video_receive_stream2.cc b/video/video_receive_stream2.cc
index 4a7e7ac..31a52aa 100644
--- a/video/video_receive_stream2.cc
+++ b/video/video_receive_stream2.cc
@@ -822,8 +822,13 @@
   if (stream_is_active && !IsReceivingKeyFrame(now) &&
       (!config_.crypto_options.sframe.require_frame_encryption ||
        rtp_video_stream_receiver_.IsDecryptable())) {
+    absl::optional<uint32_t> last_timestamp =
+        rtp_video_stream_receiver_.LastReceivedFrameRtpTimestamp();
     RTC_LOG(LS_WARNING) << "No decodable frame in " << wait
-                        << ", requesting keyframe.";
+                        << " requesting keyframe. Last RTP timestamp "
+                        << (last_timestamp ? rtc::ToString(*last_timestamp)
+                                           : "<not set>")
+                        << ".";
     RequestKeyFrame(now);
   }