Update Subset benches to support interlacing and fix bugs

Instead of decoding one line at a time, if the ScanlineOrder is kNone,
decode all of the lines in one pass, and then copy the subset into the
output. This will allow us to more realistically test subset decodes
for interlaced png. It also makes running them not take forever.

Do *not* support other modes (besides kTopDown), since they are not
used by the big three we need to replace BitmapRegionDecoder
implementation (skbug.com/4428).

Fix a bug in SubsetTranslateBench and SubsetZoomBench:
When we decode another subset, we need to reset the scanline decode
first. This bug appears to have been present since the introduction of
these tests in crrev.com/1160953002

BUG=skia:4205
BUG=skia:3418

Review URL: https://codereview.chromium.org/1387233002
4 files changed