Merged r15573 into 3.19 branch.

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
R=danno@chromium.org

Review URL: https://chromiumcodereview.appspot.com/19510003

git-svn-id: https://v8.googlecode.com/svn/branches/3.19@15706 ce2b1a6d-e550-0410-aec6-3dcde31c8c00