Thank you sammiequon@ for taking over this.

To state once again why we might want to do this: I think the biggest benefit we can get adding a filter scale to foreground blur is to reduce the time spent when Skia allocates temporary textures to apply the filter.

If you try to run a trace on nocturne when we enter overview mode, you'll notice a few 4096x4096 allocations done by skia to apply the foreground filter when we animated the blur radius.
Each of those allocations can take more than 500ms on the main GPU thread, blocking the whole system.

If we could reduce the size of the buffers Skia allocates we should be able to reduce significantly the number of dropped frames when we enter overview.

My plan was to rename the BackdropFilterQuality property we added to FilterQuality (draft: https://crrev.com/c/1403978) and then propagate it to SkiaHelper::ApplyImageFilter that is where the Skia filters are applied.