Reorganized the getter methods of SwapChain11 and added a method to get the offscreen texture shader resource.

TRAC #22358

Signed-off-by: Nicolas Capens
Signed-off-by: Shannon Woods
Author: Geoff Lang

git-svn-id: https://angleproject.googlecode.com/svn/branches/dx11proto@1742 736b8ea6-26fd-11df-bfd4-992fa37f6226