Add assert to catch circular drawing higher up the call stack.



git-svn-id: http://skia.googlecode.com/svn/trunk@3559 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/include/gpu/GrTexture.h b/include/gpu/GrTexture.h
index 8274140..8e39fb5 100644
--- a/include/gpu/GrTexture.h
+++ b/include/gpu/GrTexture.h
@@ -94,6 +94,7 @@
      *            render target
      */
     GrRenderTarget* asRenderTarget() { return fRenderTarget; }
+    const GrRenderTarget* asRenderTarget() const { return fRenderTarget; }
 
     /**
      * Removes the reference on the associated GrRenderTarget held by this