Add class GrGLTextureRenderTarget for GL texture/rendertarget objects

src/gpu/GrDrawState.h

Index: src/gpu/GrDrawState.h
diff --git a/src/gpu/GrDrawState.h b/src/gpu/GrDrawState.h
index 39c91027914138a8e6f2ca4a50b0ec5ad7004ce8..97516e80432190adc444b68cf306e55ae5a68933 100644
--- a/src/gpu/GrDrawState.h
+++ b/src/gpu/GrDrawState.h
@@ -530,9 +530,7 @@ public:
      *
      * @return    The currently set render target.
      */
-    GrRenderTarget* getRenderTarget() const {
-        return static_cast<GrRenderTarget*>(fRenderTarget.getResource());
-    }
+    GrRenderTarget* getRenderTarget() const { return fRenderTarget.get(); }
 
     /**
      * Sets the render-target used at the next drawing call