Add ability to read and write wav files using rtc::PlatformFile instead of file name. Bug: webrtc:8946 Change-Id: If18d9465f2155a33547f800edbdac45971a0e878 Reviewed-on: https://webrtc-review.googlesource.com/61424 Commit-Queue: Artem Titov <titovartem@webrtc.org> Reviewed-by: Karl Wiberg <kwiberg@webrtc.org> Cr-Commit-Position: refs/heads/master@{#22497}