PacketBuffer: remove lock recursions.

This change removes lock recursions and adds thread annotations.

Bug: webrtc:11567
Change-Id: Ibc429571926693f4b3de78f97a5dc5501d93a4a3
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/176240
Reviewed-by: Rasmus Brandt <brandtr@webrtc.org>
Commit-Queue: Markus Handell <handellm@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#31369}
diff --git a/modules/video_coding/packet_buffer.cc b/modules/video_coding/packet_buffer.cc
index 5db3c0f..d62dc84 100644
--- a/modules/video_coding/packet_buffer.cc
+++ b/modules/video_coding/packet_buffer.cc
@@ -112,7 +112,7 @@
       // Clear the buffer, delete payload, and return false to signal that a
       // new keyframe is needed.
       RTC_LOG(LS_WARNING) << "Clear PacketBuffer and request key frame.";
-      Clear();
+      ClearInternal();
       result.buffer_cleared = true;
       return result;
     }
@@ -174,16 +174,7 @@
 
 void PacketBuffer::Clear() {
   rtc::CritScope lock(&crit_);
-  for (auto& entry : buffer_) {
-    entry = nullptr;
-  }
-
-  first_packet_received_ = false;
-  is_cleared_to_first_seq_num_ = false;
-  last_received_packet_ms_.reset();
-  last_received_keyframe_packet_ms_.reset();
-  newest_inserted_seq_num_.reset();
-  missing_packets_.clear();
+  ClearInternal();
 }
 
 PacketBuffer::InsertResult PacketBuffer::InsertPadding(uint16_t seq_num) {
@@ -204,6 +195,19 @@
   return last_received_keyframe_packet_ms_;
 }
 
+void PacketBuffer::ClearInternal() {
+  for (auto& entry : buffer_) {
+    entry = nullptr;
+  }
+
+  first_packet_received_ = false;
+  is_cleared_to_first_seq_num_ = false;
+  last_received_packet_ms_.reset();
+  last_received_keyframe_packet_ms_.reset();
+  newest_inserted_seq_num_.reset();
+  missing_packets_.clear();
+}
+
 bool PacketBuffer::ExpandBufferSize() {
   if (buffer_.size() == max_size_) {
     RTC_LOG(LS_WARNING) << "PacketBuffer is already at max size (" << max_size_