Each SharedFunctionInfo gets an optimized code map to store
one optimized code object per context. When allocating a new
closure we consult this map and check if there is optimized code
that can be shared.

This patch is based on an original patch
by Anton Muhin (http://codereview.chromium.org/6793013/).

BUG=v8:2087, v8:2094
TEST=test/mjsunit/compiler/optimized-closures.js
Review URL: https://chromiumcodereview.appspot.com/10103035

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@11817 ce2b1a6d-e550-0410-aec6-3dcde31c8c00