Remove/optimize calls to BackdropFilterBounds()

With this CL, there are more early-outs in UpdateCompositorFilterOperationsForBackdropFilter
and CreateCompositorFilterOperationsForBackdropFilter in the case where
there isn't a backdrop filter present. Also combined
BackdropFilterBounds and BackdropFilterReferenceBox, as the latter was
not used anywhere else. And added a backdrop-filter test that uses
an SVG reference filter.

Bug: 497522
Change-Id: If6807f774fa0a552ee57b584839ad960fdc27189
Reviewed-on: https://chromium-review.googlesource.com/c/1393943
Reviewed-by: Stefan Zager <szager@chromium.org>
Commit-Queue: Mason Freed <masonfreed@chromium.org>
Cr-Commit-Position: refs/heads/master@{#619986}
6 files changed