Wire up RTCOutboundRtpStreamStats.totalEncodeTime.

This is a follow-up to
https://webrtc-review.googlesource.com/c/src/+/130517 that calculated
this metric.

This CL is purely plumbing, exposing
VideoSendStream::total_encode_time_ms in standard getStats() as
RTCOutboundRtpStreamStats.totalEncodeTime (in seconds):
https://w3c.github.io/webrtc-stats/#dom-rtcoutboundrtpstreamstats-totalencodetime

Bug: webrtc:10448
Change-Id: I715f1ef937e441169dee55b5e8d4fbf98811c5f3
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/131940
Reviewed-by: Steve Anton <steveanton@webrtc.org>
Commit-Queue: Henrik Boström <hbos@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#27501}
diff --git a/media/base/media_channel.h b/media/base/media_channel.h
index 617af32..b64803b 100644
--- a/media/base/media_channel.h
+++ b/media/base/media_channel.h
@@ -527,6 +527,8 @@
   int avg_encode_ms = 0;
   int encode_usage_percent = 0;
   uint32_t frames_encoded = 0;
+  // https://w3c.github.io/webrtc-stats/#dom-rtcoutboundrtpstreamstats-totalencodetime
+  uint64_t total_encode_time_ms = 0;
   bool has_entered_low_resolution = false;
   absl::optional<uint64_t> qp_sum;
   webrtc::VideoContentType content_type = webrtc::VideoContentType::UNSPECIFIED;