Reland "Fix GetStats bytesSent/Received, wireup headerBytesSent/Received"

This is a reland of fbde32e596f06893d6dda13eb7d29f4c251cf08b

The chromium problem should be fixed with
https://chromium-review.googlesource.com/c/chromium/src/+/1862437

Original change's description:
> Fix GetStats bytesSent/Received, wireup headerBytesSent/Received
>
> Changes the standard GetStats, legacy GetStats unchanged.
>
> Bug: webrtc:10525
> Change-Id: Ie10fe8079f1d8b4cc6bbe513f6a2fc91477b5441
> Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/156084
> Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
> Reviewed-by: Henrik Boström <hbos@webrtc.org>
> Reviewed-by: Harald Alvestrand <hta@webrtc.org>
> Commit-Queue: Niels Moller <nisse@webrtc.org>
> Cr-Commit-Position: refs/heads/master@{#29462}

Tbr: kwiberg@webrtc.org
Bug: webrtc:10525
Change-Id: I3b61f9535aa3f1fca2ed84f068233803d4ec9fe2
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/157045
Reviewed-by: Niels Moller <nisse@webrtc.org>
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Commit-Queue: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#29485}

pc/stats_collector.h

diff --git a/pc/stats_collector.h b/pc/stats_collector.h
index fa9d587..041fe2f 100644
--- a/pc/stats_collector.h
+++ b/pc/stats_collector.h
@@ -94,6 +94,8 @@
   // ignored.
   void ClearUpdateStatsCacheForTest();
 
+  bool UseStandardBytesStats() const { return use_standard_bytes_stats_; }
+
  private:
   friend class StatsCollectorTest;
 
@@ -143,6 +145,7 @@
   // Raw pointer to the peer connection the statistics are gathered from.
   PeerConnectionInternal* const pc_;
   double stats_gathering_started_;
+  const bool use_standard_bytes_stats_;
 
   // TODO(tommi): We appear to be holding on to raw pointers to reference
   // counted objects?  We should be using scoped_refptr here.