Added protobuf message for loss-based BWE events, and wired it up to the send side bandwidth estimator.

BUG=

Review URL: https://codereview.webrtc.org/1411673003

Cr-Original-Commit-Position: refs/heads/master@{#10531}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 006d93d3c679ffd15223c327d649066a72400639
10 files changed