Fix some sign-compare warnings in webrtc/api.

webrtc/api/webrtcsdp.cc

 /*
  *  Copyright 2011 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 2169 matching lines @@
 };
 
 void MaybeCreateStaticPayloadAudioCodecs(
     const std::vector<int>& fmts, AudioContentDescription* media_desc) {
   if (!media_desc) {
     return;
   }
   RTC_DCHECK(media_desc->codecs().empty());
   std::vector<int>::const_iterator it = fmts.begin();
   for (; it != fmts.end(); ++it) {
     int payload_type = *it;

[henrika_webrtc, 2016/06/20 13:55:55]

can't you do 

size_t payload_type = *it 

here instead

[kjellander_webrtc, 2016/06/20 14:02:26]

I tried, but line 2192 checks if it's >=0 so it seems it can be <0, which is why
I don't want to change the behavior of the code.

     if (!media_desc->HasCodec(payload_type) &&
         payload_type >= 0 &&
-        payload_type < arraysize(kStaticPayloadAudioCodecs)) {
+        static_cast<uint32_t>(payload_type) <
+            arraysize(kStaticPayloadAudioCodecs)) {
       std::string encoding_name = kStaticPayloadAudioCodecs[payload_type].name;
       int clock_rate = kStaticPayloadAudioCodecs[payload_type].clockrate;
       size_t channels = kStaticPayloadAudioCodecs[payload_type].channels;
       media_desc->AddCodec(cricket::AudioCodec(payload_type, encoding_name,
                                                clock_rate, 0, channels));
     }
   }
 }
 
 template <class C>
@@ skipping 972 matching lines @@
     UpdateCodec<AudioContentDescription, cricket::AudioCodec>(
         media_desc, payload_type, feedback_param);
   } else if (media_type == cricket::MEDIA_TYPE_VIDEO) {
     UpdateCodec<VideoContentDescription, cricket::VideoCodec>(
         media_desc, payload_type, feedback_param);
   }
   return true;
 }
 
 }  // namespace webrtc