Added ES3 validation for glReadPixels and glReadnPixelsEXT. TRAC #22956 Signed-off-by: Jamie Madill Signed-off-by: Shannon Woods Author: Geoff Lang git-svn-id: https://angleproject.googlecode.com/svn/branches/es3proto@2355 736b8ea6-26fd-11df-bfd4-992fa37f6226