Removing the redundant last_estimated_bitrate_bps_ and renaming some
members to better reflect the contents. Also replacing the CurrentEstimate
method of SendSideBandwidthEstimation with value specific access methods.
Bug: webrtc:9883
Change-Id: I73cb08e09374adddf5991cb3793fa4a4fee20c85
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/154351
Reviewed-by: Niels Moller <nisse@webrtc.org>
Commit-Queue: Sebastian Jansson <srte@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#29304}