The WebView SDK Sandbox Test App and SDK are a standalone application and sdk for testing WebView in a privacy sandbox environment. 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