Only allow throttling if object caching is enabled...

...otherwise it doesn't work.

This change add 2 checks for object caching, one for the filter
configuration interface, and one for the actual throttle checking.

Bug: 50894
Change-Id: I89ebcc6ff7d91d3a9ad8e744c0c4ff3e33e3b673
Merge "Only allow throttling if object caching is enabled..."