We have seen that PostTask can consume some CPU and the way we used it
before (logging only) in the ADB is not worth the cost we see when
profiling.
This CL simply moves frequent (trivial) stat updates from the task queue
to the native threads to avoid calling PostTask in each callback.
The reason for doing so before was to avoid locks but we can live without
them since races are benign here.
BUG=webrtc:7096
Review-Url: https://codereview.webrtc.org/2663383004
Cr-Commit-Position: refs/heads/master@{#16429}
77ce9a5541