Reland "Cleanup of video packet overhead calculation."

This is a reland of 890bc3069cbababa19b40ec02684253d60e051b2

Zero bitrate caused division by zero in DCHECK for max bitrate.
Added unit tests to ensure that setting zero bitrate does not crash.

> Original change's description:
> > Cleanup of video packet overhead calculation.
> >
> > This CL updates the video packet overhead calculation to make it more
> > clear. This prepares for future work on improving the accuracy of the
> > calculation.
> >
> > Bug: webrtc:9883
> > Change-Id: I1d623a3e0de45be7b6e4a1f9e3cbe54fd2b8a45a
> > Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/138077
> > Commit-Queue: Sebastian Jansson <srte@webrtc.org>
> > Reviewed-by: Erik Språng <sprang@webrtc.org>
> > Cr-Commit-Position: refs/heads/master@{#28040}

Bug: webrtc:10674
Change-Id: I156d1ee5546ede7e43ae1d9a298dcaba6071230f
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/140890
Reviewed-by: Niels Moller <nisse@webrtc.org>
Reviewed-by: Erik Språng <sprang@webrtc.org>
Commit-Queue: Sebastian Jansson <srte@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#28212}

call/rtp_video_sender.cc

diff --git a/call/rtp_video_sender.cc b/call/rtp_video_sender.cc
index 424c32d..eb00c48 100644
--- a/call/rtp_video_sender.cc
+++ b/call/rtp_video_sender.cc
@@ -189,19 +189,13 @@
       RTPSender::FecExtensionSizes(), rtp_state, clock);
 }
 
-uint32_t CalculateOverheadRateBps(int packets_per_second,
-                                  size_t overhead_bytes_per_packet,
-                                  uint32_t max_overhead_bps) {
-  uint32_t overhead_bps =
-      static_cast<uint32_t>(8 * overhead_bytes_per_packet * packets_per_second);
-  return std::min(overhead_bps, max_overhead_bps);
-}
-
-int CalculatePacketRate(uint32_t bitrate_bps, size_t packet_size_bytes) {
-  size_t packet_size_bits = 8 * packet_size_bytes;
-  // Ceil for int value of bitrate_bps / packet_size_bits.
-  return static_cast<int>((bitrate_bps + packet_size_bits - 1) /
-                          packet_size_bits);
+DataRate CalculateOverheadRate(DataRate data_rate,
+                               DataSize packet_size,
+                               DataSize overhead_per_packet) {
+  Frequency packet_rate = data_rate / packet_size;
+  // TOSO(srte): We should not need to round to nearest whole packet per second
+  // rate here.
+  return packet_rate.RoundUpTo(Frequency::hertz(1)) * overhead_per_packet;
 }
 }  // namespace
 
@@ -694,16 +688,17 @@
                                       int framerate) {
   // Substract overhead from bitrate.
   rtc::CritScope lock(&crit_);
+  DataSize packet_overhead = DataSize::bytes(
+      overhead_bytes_per_packet_ + transport_overhead_bytes_per_packet_);
+  DataSize max_total_packet_size = DataSize::bytes(
+      rtp_config_.max_packet_size + transport_overhead_bytes_per_packet_);
   uint32_t payload_bitrate_bps = bitrate_bps;
   if (send_side_bwe_with_overhead_) {
-    uint32_t overhead_bps = CalculateOverheadRateBps(
-        CalculatePacketRate(
-            bitrate_bps,
-            rtp_config_.max_packet_size + transport_overhead_bytes_per_packet_),
-        overhead_bytes_per_packet_ + transport_overhead_bytes_per_packet_,
-        bitrate_bps);
-    RTC_DCHECK_LE(overhead_bps, bitrate_bps);
-    payload_bitrate_bps = bitrate_bps - overhead_bps;
+    DataRate overhead_rate = CalculateOverheadRate(
+        DataRate::bps(bitrate_bps), max_total_packet_size, packet_overhead);
+    // TODO(srte): We probably should not accept 0 payload bitrate here.
+    payload_bitrate_bps =
+        rtc::saturated_cast<uint32_t>(bitrate_bps - overhead_rate.bps());
   }
 
   // Get the encoder target rate. It is the estimated network rate -
@@ -724,18 +719,20 @@
 
   loss_mask_vector_.clear();
 
-  uint32_t encoder_overhead_rate_bps =
-      send_side_bwe_with_overhead_
-          ? CalculateOverheadRateBps(
-                CalculatePacketRate(encoder_target_rate_bps_,
-                                    rtp_config_.max_packet_size +
-                                        transport_overhead_bytes_per_packet_ -
-                                        overhead_bytes_per_packet_),
-                overhead_bytes_per_packet_ +
-                    transport_overhead_bytes_per_packet_,
-                bitrate_bps - encoder_target_rate_bps_)
-          : 0;
-
+  uint32_t encoder_overhead_rate_bps = 0;
+  if (send_side_bwe_with_overhead_) {
+    // TODO(srte): The packet size should probably be the same as in the
+    // CalculateOverheadRate call above (just max_total_packet_size), it doesn't
+    // make sense to use different packet rates for different overhead
+    // calculations.
+    DataRate encoder_overhead_rate = CalculateOverheadRate(
+        DataRate::bps(encoder_target_rate_bps_),
+        max_total_packet_size - DataSize::bytes(overhead_bytes_per_packet_),
+        packet_overhead);
+    encoder_overhead_rate_bps =
+        std::min(encoder_overhead_rate.bps<uint32_t>(),
+                 bitrate_bps - encoder_target_rate_bps_);
+  }
   // When the field trial "WebRTC-SendSideBwe-WithOverhead" is enabled
   // protection_bitrate includes overhead.
   const uint32_t media_rate = encoder_target_rate_bps_ +