Fix some sign-compare warnings in webrtc/api.

webrtc/api/webrtcsdp.cc

Index: webrtc/api/webrtcsdp.cc
diff --git a/webrtc/api/webrtcsdp.cc b/webrtc/api/webrtcsdp.cc
index b2e75a21cbf911fc38273f43f1208f64357ea7c1..0b8d6f6a3d3fc28e4c4e6ba7d8de9655cc5234dc 100644
--- a/webrtc/api/webrtcsdp.cc
+++ b/webrtc/api/webrtcsdp.cc
@@ -2190,7 +2190,8 @@ void MaybeCreateStaticPayloadAudioCodecs(
     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;