Replacing Module based mechanism for processing with posting tasks.
This prepares for allowing the interval to be changed at runtime and
for removing the dependency on Module threads.
Bug: webrtc:8415
Change-Id: Iaad50466bec695be4ba26d8bd670a1981f2e0df4
Reviewed-on: https://webrtc-review.googlesource.com/60862
Commit-Queue: Sebastian Jansson <srte@webrtc.org>
Reviewed-by: Stefan Holmer <stefan@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#22406}