Call BufferStorage::markUsage when we retrieve a buffer pointer for rendering, instead of when we prepare data.

The automatic call eliminates function calls from other points in the library.

TRAC #22852

Signed-off-by: Geoff Lang
Signed-off-by: Nicolas Capens
Author: Jamie Madill

git-svn-id: https://angleproject.googlecode.com/svn/branches/es3proto@2288 736b8ea6-26fd-11df-bfd4-992fa37f6226