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

webrtc/api/udptransportinterface.h

 /*
  *  Copyright 2017 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 27 matching lines @@
   // Calling with a "nil" (default-constructed) address is legal, and unsets
   // any previously set destination.
   //
   // However, calling with an incomplete address (port or IP not set) will
   // fail.
   virtual bool SetRemoteAddress(const rtc::SocketAddress& dest) = 0;
   // Simple getter. If never set, returns nil address.
   virtual rtc::SocketAddress GetRemoteAddress() const = 0;
 };
 
+// TODO(deadbeef): Move this to .cc file and out of api/. What threads methods
+// are called on is an implementation detail.
 BEGIN_OWNED_PROXY_MAP(UdpTransport)
   PROXY_WORKER_THREAD_DESTRUCTOR()
   PROXY_WORKER_CONSTMETHOD0(rtc::SocketAddress, GetLocalAddress)
   PROXY_WORKER_METHOD1(bool, SetRemoteAddress, const rtc::SocketAddress&)
   PROXY_WORKER_CONSTMETHOD0(rtc::SocketAddress, GetRemoteAddress)
 END_PROXY_MAP()
 
 }  // namespace webrtc
 
 #endif  // WEBRTC_API_UDPTRANSPORTINTERFACE_H_