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

webrtc/api/rtpsenderinterface.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 29 matching lines @@
   // TODO(deadbeef): Remove? With GetParameters this should be redundant.
   virtual uint32_t ssrc() const = 0;
 
   // Audio or video sender?
   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;
 
+  // Returns a list of streams associated with this sender's track. Although we
+  // only support one track per stream, in theory the API allows for multiple.
   virtual std::vector<std::string> stream_ids() const = 0;
 
   virtual RtpParameters GetParameters() const = 0;
+  // Note that only a subset of the parameters can currently be changed. See
+  // rtpparameters.h
   virtual bool SetParameters(const RtpParameters& parameters) = 0;
 
   // Returns null for a video sender.
   virtual rtc::scoped_refptr<DtmfSenderInterface> GetDtmfSender() const = 0;
 
  protected:
   virtual ~RtpSenderInterface() {}
 };
 
 // Define proxy for RtpSenderInterface.
+// 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(RtpSender)
   PROXY_SIGNALING_THREAD_DESTRUCTOR()
   PROXY_METHOD1(bool, SetTrack, MediaStreamTrackInterface*)
   PROXY_CONSTMETHOD0(rtc::scoped_refptr<MediaStreamTrackInterface>, track)
   PROXY_CONSTMETHOD0(uint32_t, ssrc)
   PROXY_CONSTMETHOD0(cricket::MediaType, media_type)
   PROXY_CONSTMETHOD0(std::string, id)
   PROXY_CONSTMETHOD0(std::vector<std::string>, stream_ids)
   PROXY_CONSTMETHOD0(RtpParameters, GetParameters);
   PROXY_METHOD1(bool, SetParameters, const RtpParameters&)
   PROXY_CONSTMETHOD0(rtc::scoped_refptr<DtmfSenderInterface>, GetDtmfSender);
 END_PROXY_MAP()
 
 }  // namespace webrtc
 
 #endif  // WEBRTC_API_RTPSENDERINTERFACE_H_