Add feature for decreasing ProcessingAudioFifo size

If ChromeWideEchoCancellation is enabled, we now use the
DecreaseProcessingAudioFifoSize experiment to set the size of the
ProcessingAudioFifo. If the experiment is disabled, the size defaults
to 110.

This simultaneously removes the
kChromeWideEchoCancellationProcessingFifoSize parameter from the
ChromeWideEchoCancellation feature. This parameter is always set to
110 today, so this CL does not change existing behaviour.

Bug: 1420568
Change-Id: Ic344cf30b04a5ca3ee011b387999fb5572185afe
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4356940
Reviewed-by: Olga Sharonova <olka@chromium.org>
Reviewed-by: Thomas Guilbert <tguilbert@chromium.org>
Commit-Queue: Fredrik Hernqvist <fhernqvist@google.com>
Cr-Commit-Position: refs/heads/main@{#1120815}