MIPS: Do not omit the write-barrier if the input value is a smi.
MIPS: Do not omit the write-barrier if the input value is a smi.

Port r15573 (3954d53)

Original commit message:
ARM: Do not omit the write-barrier if the input value is a smi.
The input value isn't what is written into the field if the representation is double. A heap-number is written to the field instead; which requires a write-barrier.

BUG=chromium:254570

Review URL: https://codereview.chromium.org/18118010
Patch from Balazs Kilvady <kilvadyb@homejinni.com>.

git-svn-id: b158db1e4b4ab85d4c9e510fdef4b1e8c614b15b@15577 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

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