arm: Move unrolled array initialization to Assembler.

arm: Move unrolled array initialization to Assembler.

This is the final preparation before adding write barrier verification infrastructure on ARM
(which requires all pointer writes to pass through write-barrier aware code).

R=zra@google.com

Committed: https://code.google.com/p/dart/source/detail?r=41914

[zra, 2014-11-21 17:45:40]

lgtm

[koda, 2014-11-21 18:09:44]

Committed patchset #1 (id:1) manually as r41914 (presubmit successful).