In the #481 we established that from accessibility point of view it's best to not restrict maximum-scale and user-scaleable.

We will thus only require width=device-width and minimum-scale=1. All other properties will be left up to publisher and specific viewer implementation.

We still have to require width and minimum-scale to get GPU rasterization as described here: https://www.chromium.org/developers/design-documents/chromium-graphics/how-to-get-gpu-rasterization