The WebView shell is a standalone application for testing WebView. For more information, please see the documentation.
This is not a production quality browser and does not implement suitable security UI to be used for anything other than testing WebView. This should not be shipped anywhere or used as the basis for implementing a browser.
To build a full-fledged browser for Android, we'd recommend building Chromium for Android instead of using WebView: https://www.chromium.org/developers/how-tos/android-build-instructions