Refactor FourByteInterps. Add 64-bit Fast version. Add tests.

Refactor FourByteInterps.  Add 64-bit Fast version.  Add tests.

Effect on benches (only _fast_ should be affected, and only on 64-bit):

Desktop (64-bit)
four_byte_interp_slow_255 NONRENDERING c          7.80       7.84      -0.04    -0.5% 
four_byte_interp_slow_256 NONRENDERING c          7.38       7.36      +0.02    +0.3% 
four_byte_interp_fast_256 NONRENDERING c          4.86       4.38      +0.48    +9.9% 
four_byte_interp_fast_255 NONRENDERING c          5.80       5.16      +0.64   +11.0% 

N5 (32-bit)
four_byte_interp_slow_256 NONRENDERING c         22.22      22.66      -0.44    -2.0% 
four_byte_interp_fast_255 NONRENDERING c         22.22      22.22      +0.00    +0.0% 
four_byte_interp_fast_256 NONRENDERING c         18.81      18.81      +0.00    +0.0% 
four_byte_interp_slow_255 NONRENDERING c         22.42      22.42      +0.00    +0.0% 

BUG=

Committed: http://code.google.com/p/skia/source/detail?r=12468

[reed1, 2013-12-03 17:32:23]

lgtm

next step: remove non-fast callers?

[mtklein, 2013-12-03 18:33:42]

On 2013/12/03 17:32:23, reed1 wrote:
> lgtm
> 
> next step: remove non-fast callers?

Yep.  Figured that'd be catastrophically invasive to GMs, layout tests, etc, so
it's a follow up.

[commit-bot: I haz the power, 2013-12-03 18:34:15]

CQ is trying da patch. Follow status at
https://skia-tree-status.appspot.com/cq/mtklein@google.com/100923003/1

[commit-bot: I haz the power, 2013-12-03 18:53:32]

Change committed as 12468