The constants are reordered to match the order they are used when a sample is inserted into the filter. Some of the constants are renamed to better describe their usage. No functional changes are intended. Future CLs will add configurability to some of these constants. Some basic unit tests are also added. Bug: webrtc:14151 Change-Id: I731a9cad3d8aeab06ccfa7d212cd160a2d2da27b Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/274122 Commit-Queue: Rasmus Brandt <brandtr@webrtc.org> Reviewed-by: Philip Eliasson <philipel@webrtc.org> Cr-Commit-Position: refs/heads/main@{#38019}