Reland of Rename RTPVideoHeader.isFirstPacket to .is_first_packet_in_frame.

webrtc/modules/include/module_common_types.h

Index: webrtc/modules/include/module_common_types.h
diff --git a/webrtc/modules/include/module_common_types.h b/webrtc/modules/include/module_common_types.h
index 80c7b24732948c5f93c5a59b0a35914fbd3a39e1..513411a791eacd3e8a451285183313d6f30658a5 100644
--- a/webrtc/modules/include/module_common_types.h
+++ b/webrtc/modules/include/module_common_types.h
@@ -58,7 +58,10 @@ struct RTPVideoHeader {
 
   PlayoutDelay playout_delay;
 
-  bool isFirstPacket;    // first packet in frame
+  union {
+    bool is_first_packet_in_frame;
+    RTC_DEPRECATED bool isFirstPacket;  // first packet in frame
+  };
   uint8_t simulcastIdx;  // Index if the simulcast encoder creating
                          // this frame, 0 if not using simulcast.
   RtpVideoCodecTypes codec;