Improve documentation for ArrayView
Improve documentation for ArrayView

Review URL: https://codereview.webrtc.org/1468183003

Cr-Original-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#10775}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: c3ddb3e127a9821419671aef96f285a29d70781d

Alkalyne/webrtctrunk,aleonliao/webrtc-trunk,jchavanton/webrtc,Alkalyne/webrtctrunk,aleonliao/webrtc-trunk,jchavanton/webrtc,Alkalyne/webrtctrunk,jchavanton/webrtc,Alkalyne/webrtctrunk,aleonliao/webrtc-trunk,aleonliao/webrtc-trunk,jchavanton/webrtc,Alkalyne/webrtctrunk,jchavanton/webrtc,Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,jchavanton/webrtc,jchavanton/webrtc,Alkalyne/webrtctrunk,aleonliao/webrtc-trunk,aleonliao/webrtc-trunk