Revert of Rename RTPVideoHeader.isFirstPacket to .is_first_packet_in_frame.

webrtc/modules/rtp_rtcp/source/rtp_format_vp9.cc

 /*
  *  Copyright (c) 2015 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 710 matching lines @@
     if (!ParseSsData(&parser, vp9)) {
       LOG(LS_ERROR) << "Failed parsing VP9 SS data.";
       return false;
     }
     if (vp9->spatial_layer_resolution_present) {
       // TODO(asapersson): Add support for spatial layers.
       parsed_payload->type.Video.width = vp9->width[0];
       parsed_payload->type.Video.height = vp9->height[0];
     }
   }
-  parsed_payload->type.Video.is_first_packet_in_frame =
+  parsed_payload->type.Video.isFirstPacket =
       b_bit && (!l_bit || !vp9->inter_layer_predicted);
 
   uint64_t rem_bits = parser.RemainingBitCount();
   assert(rem_bits % 8 == 0);
   parsed_payload->payload_length = rem_bits / 8;
   if (parsed_payload->payload_length == 0) {
     LOG(LS_ERROR) << "Failed parsing VP9 payload data.";
     return false;
   }
   parsed_payload->payload =
       payload + payload_length - parsed_payload->payload_length;
 
   return true;
 }
 }  // namespace webrtc