WebView fallback

Investigate providing a WebView fallback when the device does not have a TWA provider.

• Have a look at current usage.
• Consider APK size increase.
• Consider WebView Web API support.

Requirements for a WebView fallback:

• Opens startUrl in full-screen
• Supports multiple Origins
• Handles external navigations using CustomTabs
• New Intents should re-use an existing Activity / WebView
• Handle orientation changes so that page state isn’t lost
• Handle onPause/onResume
• Handle onBackPressed
• Handle onSaveInstanceState
• Enable domstorage, database, etc.
• Splash screen support
• Immersive mode
• Sets android-app://<package-id> referrer.

[andreban]

I’ve just added support for earlier APIs on the last PR.

Regarding Fire TV / Android TV, my guess is that developers should probably use store targeting to deploy a different APK that uses the WebView in those platforms. I don’t know about Fire TV, but Android TV doesn’t come with a browser. And Chrome can’t be installed from the store.

I’ll check out the best approach for the others.

[andreban]

I think an approach we can take here is to add a demo app that contains a WebView fallback. We can start with a naive implementation that will give us more understanding on what we will need to do to have solid implementation in the library and, once we are happy we can move the implementation there.

@PEConn, WDYT? @b1tr0t, FYI