This is related to feature detection in the WebView Support Library:

it would be great to be able to communicate what features are available app developers through just letting them know which is the effective Android version of the current device setup (and WebView support library). However, there are some features that are tied to a specific Android version - and such features thus won't be available if the device Android version is lower than that, even though the WebView APK supports a higher 'effective Android version'.

We should scope out what these features are to ensure there aren't too many of them.