message: Add some RTC_GUARDED_BY statements
  These seem to have been forgotten when modifying
  sdp_offer_answer.h. It's nice to be consistent.
  Cr-Commit-Position: refs/heads/main@{#35243}
diff: @@ -555,6 +555,15 @@ class SdpOfferAnswerHandler : public SdpStateProvider,
  const std::map<std::string, const cricket::ContentGroup*>&
  bundle_groups_by_mid);
  + // Updates the error state, signaling if necessary.
  + void SetSessionError(SessionError error, const std::string& error_desc);
  +
  + // Implements AddIceCandidate without reporting usage, but returns the
  + // particular success/error value that should be reported (and can be utilized
  + // for other purposes).
  + AddIceCandidateResult AddIceCandidateInternal(
  + const IceCandidateInterface* candidate);
  +
  // ==================================================================
  // Access to pc_ variables
  cricket::ChannelManager* channel_manager() const;
  @@ -627,14 +636,16 @@ class SdpOfferAnswerHandler : public SdpStateProvider,
  bool remote_peer_supports_msid_ RTC_GUARDED_BY(signaling_thread()) = false;
  bool is_negotiation_needed_ RTC_GUARDED_BY(signaling_thread()) = false;
  - uint32_t negotiation_needed_event_id_ = 0;
  + uint32_t negotiation_needed_event_id_ RTC_GUARDED_BY(signaling_thread()) = 0;
  bool update_negotiation_needed_on_empty_chain_
  RTC_GUARDED_BY(signaling_thread()) = false;
  // If PT demuxing is successfully negotiated one time we will allow PT
  // demuxing for the rest of the session so that PT-based apps default to PT
  // demuxing in follow-up O/A exchanges.
  - bool pt_demuxing_has_been_used_audio_ = false;
  - bool pt_demuxing_has_been_used_video_ = false;
  + bool pt_demuxing_has_been_used_audio_ RTC_GUARDED_BY(signaling_thread()) =
  + false;
  + bool pt_demuxing_has_been_used_video_ RTC_GUARDED_BY(signaling_thread()) =
  + false;
  // In Unified Plan, if we encounter remote SDP that does not contain an a=msid
  // line we create and use a stream with a random ID for our receivers. This is
  @@ -643,15 +654,6 @@ class SdpOfferAnswerHandler : public SdpStateProvider,
  rtc::scoped_refptr<MediaStreamInterface> missing_msid_default_stream_
  RTC_GUARDED_BY(signaling_thread());
  - // Updates the error state, signaling if necessary.
  - void SetSessionError(SessionError error, const std::string& error_desc);
  -
  - // Implements AddIceCandidate without reporting usage, but returns the
  - // particular success/error value that should be reported (and can be utilized
  - // for other purposes).
  - AddIceCandidateResult AddIceCandidateInternal(
  - const IceCandidateInterface* candidate);
  -
  SessionError session_error_ RTC_GUARDED_BY(signaling_thread()) =
  SessionError::kNone;
  std::string session_error_desc_ RTC_GUARDED_BY(signaling_thread());
  @@ -674,7 +676,7 @@ class SdpOfferAnswerHandler : public SdpStateProvider,
  // Note that one can still choose to override this in a MediaEngine
  // if one wants too.
  std::unique_ptr<webrtc::VideoBitrateAllocatorFactory>
  - video_bitrate_allocator_factory_;
  + video_bitrate_allocator_factory_ RTC_GUARDED_BY(signaling_thread());
  rtc::WeakPtrFactory<SdpOfferAnswerHandler> weak_ptr_factory_
  RTC_GUARDED_BY(signaling_thread());
  