Move skp nanobench tile size back to 256x256 to see if it fixes nanobench crashes

Move skp nanobench tile size back to 256x256 to see if it fixes nanobench crashes

Going back to old nanobench tile size to see if the increase to tile is what has been
causing recent nanobench crashes. The crashes seem very nondeterministic and hard to
debug manually.

256x256 is too small of a tile to give accurate gpu results but if this fixes we can try some compromise in the middle 

BUG=skia:

Committed: https://skia.googlesource.com/skia/+/5d09568a0c67bc54dfb38552d0136b06d3ebf018

[egdaniel, 2015-03-19 17:39:43]

egdaniel@google.com changed reviewers:
+ bsalomon@google.com, joshualitt@google.com, robertphillips@google.com

[robertphillips, 2015-03-19 17:45:50]

lgtm

[egdaniel, 2015-03-19 17:46:02]

The CQ bit was checked by egdaniel@google.com

[commit-bot: I haz the power, 2015-03-19 17:46:15]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1022823003/1

[brian1, 2015-03-19 17:46:36]

On 2015/03/19 17:39:43, egdaniel wrote:

Ok as an experiment but I'd rather disable nb on this bot than gather data that
doesnt reflect chrome on all bots

[commit-bot: I haz the power, 2015-03-19 18:00:14]

Committed patchset #1 (id:1) as
https://skia.googlesource.com/skia/+/5d09568a0c67bc54dfb38552d0136b06d3ebf018

[egdaniel, 2015-03-19 18:00:53]

On 2015/03/19 17:46:36, brian1 wrote:
> On 2015/03/19 17:39:43, egdaniel wrote:
> 
> Ok as an experiment but I'd rather disable nb on this bot than gather data
that
> doesnt reflect chrome on all bots

yeah this won't be a long term solution, just to see what happens. If lowering
the tile sizes fixes the crashes, all that is saying is smaller tiles are
covering up some other bug in our code. We would still want to figure out the
bug so that larger tiles can be used.

[mtklein, 2015-03-19 18:01:25]

On 2015/03/19 17:46:36, brian1 wrote:
> On 2015/03/19 17:39:43, egdaniel wrote:
> 
> Ok as an experiment but I'd rather disable nb on this bot than gather data
that
> doesnt reflect chrome on all bots

We can also just set the tiles to 256x256 for this bot, by setting --benchTileW
/ --benchTileH in tools/nanobench_flags.py.