I find the browser complaint funny because they've moved to Chrome which even has an open development model[1] (Android does not). Chrome is also used for the WebView implementation starting in KitKat[2] (made updateable via Play Store in Lollipop). All of this code is open-source and also openly developed (which means code review, bug tracker, mailing lists, design docs are public).

[1] https://news.ycombinator.com/item?id=12578134

[2] https://developer.chrome.com/multidevice/webview/overview