Trac #22229

Uses a 12-entry LRU cache to avoid recreating them unnecessarily.

Signed-off-by: Nicolas Capens
Signed-off-by: Shannon Woods

git-svn-id: https://angleproject.googlecode.com/svn/branches/dx11proto@1567 736b8ea6-26fd-11df-bfd4-992fa37f6226