Added an abstract Renderer::clear method.

TRAC #22041

Unimplemented in Renderer11 and Renderer9 only forces the depth stencil state
to reset.

Signed-off-by: Shannon Woods
Signed-off-by: Daniel Koch

Author:    Geoff Lang

git-svn-id: https://angleproject.googlecode.com/svn/branches/dx11proto@1423 736b8ea6-26fd-11df-bfd4-992fa37f6226
6 files changed