Adding more comments to every header file in api/ subdirectory.

webrtc/api/rtpreceiverinterface.h

 /*
  *  Copyright 2015 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 36 matching lines @@
   virtual cricket::MediaType media_type() const = 0;
 
   // Not to be confused with "mid", this is a field we can temporarily use
   // to uniquely identify a receiver until we implement Unified Plan SDP.
   virtual std::string id() const = 0;
 
   // The WebRTC specification only defines RTCRtpParameters in terms of senders,
   // but this API also applies them to receivers, similar to ORTC:
   // http://ortc.org/wp-content/uploads/2016/03/ortc.html#rtcrtpparameters*.
   virtual RtpParameters GetParameters() const = 0;
+  // Currently, doesn't support changing any parameters, but may in the future.
   virtual bool SetParameters(const RtpParameters& parameters) = 0;
 
   // Does not take ownership of observer.
   // Must call SetObserver(nullptr) before the observer is destroyed.
   virtual void SetObserver(RtpReceiverObserverInterface* observer) = 0;
 
  protected:
   virtual ~RtpReceiverInterface() {}
 };
 
 // Define proxy for RtpReceiverInterface.
+// TODO(deadbeef): Move this to .cc file and out of api/. What threads methods
+// are called on is an implementation detail.
 BEGIN_SIGNALING_PROXY_MAP(RtpReceiver)
   PROXY_SIGNALING_THREAD_DESTRUCTOR()
   PROXY_CONSTMETHOD0(rtc::scoped_refptr<MediaStreamTrackInterface>, track)
   PROXY_CONSTMETHOD0(cricket::MediaType, media_type)
   PROXY_CONSTMETHOD0(std::string, id)
   PROXY_CONSTMETHOD0(RtpParameters, GetParameters);
   PROXY_METHOD1(bool, SetParameters, const RtpParameters&)
   PROXY_METHOD1(void, SetObserver, RtpReceiverObserverInterface*);
 END_PROXY_MAP()
 
 }  // namespace webrtc
 
 #endif  // WEBRTC_API_RTPRECEIVERINTERFACE_H_