Use a fixed input register where we require a byte register.
Use a fixed input register where we require a byte register.

Currently we can't specify a set of registers as a register constraint.
This change forces a fixed register (eax) in places that need
a byte register.

BUG=77752
Review URL: http://codereview.chromium.org/6708109

git-svn-id: b158db1e4b4ab85d4c9e510fdef4b1e8c614b15b@7417 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

UniversalFuture/moosh,UniversalFuture/moosh,UniversalFuture/moosh,UniversalFuture/moosh