Beta Channel for the Android WebView
http://android-developers.blogspot.co.uk/2015/02/beta-channel-for-android-webview.html
WebView Beta Channel
https://plus.google.com/communities/105434725573080290360
ub-webview-m40-release in AOSP
https://groups.google.com/forum/?nomobile=true#!topic/android-building/1vViZA9UH_I
ライブラリのソースも公開。