Change signatures of filter bounds methods to return a rect.

Change signatures of filter bounds methods to return a rect.

Change filterBounds(), onFilterBounds() and onFilterNodeBounds() and computeFastBounds() to
return the destination rectangle. There was no code path that could
return false, and returning rects by value is ok now.

BUG=skia:5094
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Review URL: https://codereview.chromium.org/1823573003