2 Moar optimizations to SyzyASan ! (Slow path only)
2 Moar optimizations to SyzyASan ! (Slow path only)

1) We can use the fact that the shadow non accessible byte mask is a signed negative value to remove one instruction from the slow path.
2) In the slow path we can use DH instead of EAX. This save a push/pop eax.

This bring a 2% perf improvement...

This CL:
609.10runs/s : http://dromaeo.com/?id=195572
607.13runs/s : http://dromaeo.com/?id=195573
605.65runs/s : http://dromaeo.com/?id=195574
Avg: 607.29

master@r1527:
602.75runs/s : http://dromaeo.com/?id=195575
586.02runs/s : http://dromaeo.com/?id=195578
597.39runs/s : http://dromaeo.com/?id=195577
Avg: 595.39

R=siggi@chromium.org

BUG=

Review URL: https://codereview.appspot.com/9666043

git-svn-id: db59699583a60be9a535cd09cdc9132301867226@1529 15e8cca8-e42c-11de-a347-f34a4f72eb7d

pombreda/syzygy,ericmckean/syzygy,supriyantomaftuh/syzygy,sebmarchand/syzygy,supriyantomaftuh/syzygy,ericmckean/syzygy,ericmckean/syzygy,google/syzygy,wangming28/syzygy,pombreda/syzygy,wangming28/syzygy,google/syzygy,supriyantomaftuh/syzygy,sebmarchand/syzygy,wangming28/syzygy,sebmarchand/syzygy,ericmckean/syzygy,ericmckean/syzygy,google/syzygy,pombreda/syzygy,sebmarchand/syzygy,wangming28/syzygy,pombreda/syzygy,Eloston/syzygy,supriyantomaftuh/syzygy,sebmarchand/syzygy,google/syzygy,Eloston/syzygy,pombreda/syzygy