Make UsePosition::hint immutable.

R=svenpanne@chromium.org

Review URL: https://codereview.chromium.org/14524008

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@14489 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Flag optimize-constructed-arrays turned on.

This routes array construction through a hydrogen stub, and enables use of
allocation site info tracking.

BUG=

Review URL: https://codereview.chromium.org/14616010

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@14490 ce2b1a6d-e550-0410-aec6-3dcde31c8c00