When guessing at the dest, use linear space instead of color space.

[bungeman, 2012-03-02 21:58:20]

This change fixes colors like 0x004276 since they should be rendered against
something fairly bright, as opposed to the fairly dark 0xFFAAAAAA. Since this is
done in linear space the actual color space is immaterial.

[reed1, 2012-03-02 22:08:11]

lgtm

1. might document why we use 66,99 instead of 55,AA for the middle two
2. remove the SkDebugf

[bungeman, 2012-03-13 13:51:59]

On 2012/03/02 22:08:11, reed1 wrote:
> lgtm
> 
> 1. might document why we use 66,99 instead of 55,AA for the middle two
> 2. remove the SkDebugf

Committed revision r3313.
Rebaselined r3314.