Replace OS::MemCopy with memcpy in typed array initialization.
Replace OS::MemCopy with memcpy in typed array initialization.

This is an attempt to fix a weird perf regression on MacOS X 10.6 bot.
Perf regression is not reproducible on MacOS X 10.8.
This difference in memory-copying routines is the only reasonable
difference in the algorithm. We should try and see.

R=bmeurer@chromium.org
BUG=270642

Review URL: https://codereview.chromium.org/23330005

git-svn-id: b158db1e4b4ab85d4c9e510fdef4b1e8c614b15b@16245 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

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