Fix for rounded-rect clips with filters.

Fix for rounded-rect clips with filters.

Don't use the base canvas size to limit raster of complex clips, since
the top canvas size may actually be larger (e.g., a blur filter which
expands the clip bounds to accommodate filter margins). Use the top
canvas bounds instead.

BUG=skia:4879,471212
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Review URL: https://codereview.chromium.org/1657333002