Add reporting of googContentType via GetStats on send side

BUG=webrtc:8174

Review-Url: https://codereview.webrtc.org/3005193002
Cr-Original-Commit-Position: refs/heads/master@{#19719}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 50864a8f4b911cce51aec715985a929cad86c688
5 files changed