Add --nameByHash for the bots, and refactor hashing a bit.

Add --nameByHash for the bots, and refactor hashing a bit.

No diff in dm.json output.

Here's what we get when --nameByHash is on:

mtklein@mtklein ~/skia (dm)> ls bad4/
0077fefedcee39feae9d12751853758b.png  431921de1607b4e1ae6864cc684d9b8e.png  8a3e17eba9302498700a703bb286d1ef.png  c6448cb266f5e0b8d02b512ad484a9ad.png
01b0dcd515e846ea3b7f3b4c68120943.png  4372eb0fce0b0bcf5a582c502f90ecef.png  8a6acdd96cf6915fa01a9cea6d6291b0.png  c6db4e2c9860b900130af429373eafaa.png
02974ab0efa7aa325b3bf22515b33899.png  43bddc2e255a3501ce2728544b1d409d.png  8aa8763d11afd397c2768e54d5599181.png  c716a9a53513a16e0572c67863e3be08.png
02b7b9e5e95e69f89b6cec9c4539d972.png  43cf7adda66b3719e4abd19e92dda55e.png  8ade6bb4c9e2244e0dbd9436cf6e2132.png  c854bb6dd105644a71d0219025409039.png
02d29dbfd29260f9318fcd6177c6ba7b.png  4423958139a2b64185583dacb7379b13.png  8b039171593685112a9454879f40a965.png  c863ac2394e519690c57e1392b14b19f.png
...

BUG=skia:

Committed: https://skia.googlesource.com/skia/+/858baf5b7da669f88ab8c8cf08b5230432a174a0

[mtklein, 2014-09-08 17:52:18]

mtklein@google.com changed reviewers:
+ jcgregorio@google.com, mtklein@google.com

[jcgregorio, 2014-09-08 18:19:00]

On 2014/09/08 17:52:19, mtklein wrote:

LGTM

[mtklein, 2014-09-08 18:25:35]

The CQ bit was checked by mtklein@google.com

[commit-bot: I haz the power, 2014-09-08 18:25:56]

CQ is trying da patch. Follow status at
 https://skia-tree-status.appspot.com/cq/mtklein@chromium.org/550283002/20001

[commit-bot: I haz the power, 2014-09-08 18:33:51]

Committed patchset #2 (id:20001) as 858baf5b7da669f88ab8c8cf08b5230432a174a0