Stand-alone WebView has channel "unknown". This shows up on the histograms dashboard:

https://uma.googleplex.com/p/android_webview/histograms/?endDate=20180822&dayCount=1&histograms=UMA.RecordsCounts&fixupData=true&showMax=true&filters=channel%2Ceq%2C0%2Cisofficial%2Ceq%2CTrue&implicitFilters=isofficial

but there's no data on the timeline dashboard:

https://uma.googleplex.com/p/android_webview/timeline_v2/?sid=7d4dcb63586fcb55ebb694779c6f67ff