Respond to changes in throttle policy.

We were updating limits and such before, but we were not applying them
to the current situation if we were already throttled.  Now it can result in
us throttling or changing our throttle rate or unthrottling or even making
the ui come or go (disabling/enable throttling)

bug:2622543
bug:2619879
Change-Id: I64a62634d54f4768ab8625f8d72f9f66a239cb19