After this CL, WebRTC clients will be able to exclude the default
metrics implementation by defining the preprocessor macro
WEBRTC_EXCLUDE_METRICS_DEFAULT (if GN is used, it will be enough
to set rtc_exclude_metrics_default to true).
Bug: webrtc:9631
Change-Id: Id6db23cc4b6c292d9f97372a8014c0c467ed0538
No-Try: True
Reviewed-on: https://webrtc-review.googlesource.com/98102
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#24747}
