Revert of Rename RTPVideoHeader.isFirstPacket to .is_first_packet_in_frame.

webrtc/modules/video_coding/packet_buffer.cc

 /*
  *  Copyright (c) 2016 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 85 matching lines @@
       if (sequence_buffer_[index].used) {
         delete[] packet->dataPtr;
         packet->dataPtr = nullptr;
         return false;
       }
     }
 
     if (AheadOf(seq_num, last_seq_num_))
       last_seq_num_ = seq_num;
 
-    sequence_buffer_[index].frame_begin = packet->is_first_packet_in_frame;
+    sequence_buffer_[index].frame_begin = packet->isFirstPacket;
     sequence_buffer_[index].frame_end = packet->markerBit;
     sequence_buffer_[index].seq_num = packet->seqNum;
     sequence_buffer_[index].continuous = false;
     sequence_buffer_[index].frame_created = false;
     sequence_buffer_[index].used = true;
     data_buffer_[index] = *packet;
     packet->dataPtr = nullptr;
 
     found_frames = FindFrames(seq_num);
   }
@@ skipping 176 matching lines @@
 int PacketBuffer::Release() const {
   int count = rtc::AtomicOps::Decrement(&ref_count_);
   if (!count) {
     delete this;
   }
   return count;
 }
 
 }  // namespace video_coding
 }  // namespace webrtc