Improve documentation for ArrayView Review URL: https://codereview.webrtc.org/1468183003 Cr-Original-Commit-Position: refs/heads/master@{#10775} Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc Cr-Mirrored-Commit: c3ddb3e127a9821419671aef96f285a29d70781d