Fix dst bound reported by SkTileImageFilter

In the example from the bug we had the filter DAG:

color filter (table)
    0: xfermode filter (arith)
        0: tile filter [0,80,34,114] -> [0,80,800,480]
             0: color filter (table)
                 0: bitmap src 34x34 -> [0,80,34,114]
        1: color filter (table)
             0: picture filter [0, 80, 800, 480]

computeFastBounds was coming out of the DAG with a bound of [0,80,34,114] which didn't represent the pixels that would be drawn.

This CL updates SkTileImageFilter to correctly set the bound for the pixels it will hit.

BUG=493783

Review URL: https://codereview.chromium.org/1152553006
5 files changed