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

webrtc/modules/interface/module_common_types.h

Index: webrtc/modules/interface/module_common_types.h
diff --git a/webrtc/modules/interface/module_common_types.h b/webrtc/modules/interface/module_common_types.h
index 5ea6824b960a2275e5e6355bf76790467e64e32c..45e93d8fad3d14fb982e38885e70736f1676db97 100644
--- a/webrtc/modules/interface/module_common_types.h
+++ b/webrtc/modules/interface/module_common_types.h
@@ -131,7 +131,7 @@
       temporal_idx[i] = src.temporal_idx[i];
       temporal_up_switch[i] = src.temporal_up_switch[i];
       num_ref_pics[i] = src.num_ref_pics[i];
-      for (uint8_t r = 0; r < num_ref_pics[i]; ++r) {
+      for (size_t r = 0; r < num_ref_pics[i]; ++r) {
         pid_diff[i][r] = src.pid_diff[i][r];
       }
     }
@@ -140,8 +140,8 @@
   size_t num_frames_in_gof;
   uint8_t temporal_idx[kMaxVp9FramesInGof];
   bool temporal_up_switch[kMaxVp9FramesInGof];
-  uint8_t num_ref_pics[kMaxVp9FramesInGof];
-  uint8_t pid_diff[kMaxVp9FramesInGof][kMaxVp9RefPics];
+  size_t num_ref_pics[kMaxVp9FramesInGof];
+  int16_t pid_diff[kMaxVp9FramesInGof][kMaxVp9RefPics];
 };
 
 struct RTPVideoHeaderVP9 {
@@ -185,9 +185,9 @@
 
   uint8_t gof_idx;  // Index to predefined temporal frame info in SS data.
 
-  uint8_t num_ref_pics;  // Number of reference pictures used by this layer
-                         // frame.
-  uint8_t pid_diff[kMaxVp9RefPics];  // P_DIFF signaled to derive the PictureID
+  size_t num_ref_pics;  // Number of reference pictures used by this layer
+                        // frame.
+  int16_t pid_diff[kMaxVp9RefPics];  // P_DIFF signaled to derive the PictureID
                                      // of the reference pictures.
   int16_t ref_picture_id[kMaxVp9RefPics];  // PictureID of reference pictures.