The browser.ui.zoom.force-user-scalable pref can be modified by the user from
the Fennec settings screen, and allows them zoom pages despite the meta-viewport
tag that might otherwise restrict zooming. This effectively ignores the effect
of the user-scalable, minimum-scale, and maximum-scale meta-viewport tokens.
In the C++ APZ implementation this has no effect, because the min/max zoom values
are never even read if zooming is not allowed. When this is hooked up to the
Java implementation though, the code expects the min/max zoom values to be
equal to the default zoom values in the case where zooming is not allowed. This
behaviour change therefore facilitates hooking up the ZoomConstraintsClient
to the Java pan/zoom controller implementation, which happens in a future patch.
This aligns the code in the ZoomConstraintsClient with the other code in the
MobileViewportManager. That way they should always end up with the same result
for the CSS viewport.
