Change type of pid_diff (int16_t -> uint8_t) according to updates in RTP payload profile.

webrtc/modules/video_coding/main/source/session_info.cc

Index: webrtc/modules/video_coding/main/source/session_info.cc
diff --git a/webrtc/modules/video_coding/main/source/session_info.cc b/webrtc/modules/video_coding/main/source/session_info.cc
index 9a1bc54e5292cee8ba5804e31e7ca93d9d1cc248..1e6af8b4275ac9c736e92e4cd01ef16c07b507cb 100644
--- a/webrtc/modules/video_coding/main/source/session_info.cc
+++ b/webrtc/modules/video_coding/main/source/session_info.cc
@@ -126,7 +126,7 @@ void VCMSessionInfo::SetGofInfo(const GofInfoVP9& gof_info, size_t idx) {
       gof_info.temporal_up_switch[idx];
   packets_.front().codecSpecificHeader.codecHeader.VP9.num_ref_pics =
       gof_info.num_ref_pics[idx];
-  for (size_t i = 0; i < gof_info.num_ref_pics[idx]; ++i) {
+  for (uint8_t i = 0; i < gof_info.num_ref_pics[idx]; ++i) {
     packets_.front().codecSpecificHeader.codecHeader.VP9.pid_diff[i] =
         gof_info.pid_diff[idx][i];
   }