Enable blend optimizations with instanced draws

src/gpu/GrDrawContextPriv.h

Index: src/gpu/GrDrawContextPriv.h
diff --git a/src/gpu/GrDrawContextPriv.h b/src/gpu/GrDrawContextPriv.h
index 8087bcf58827ec91f2a7a6dc27f7974128209963..c77d8e488b461d7aa3fc79ed8918b820812682b9 100644
--- a/src/gpu/GrDrawContextPriv.h
+++ b/src/gpu/GrDrawContextPriv.h
@@ -9,6 +9,7 @@
 #define GrDrawContextPriv_DEFINED
 
 #include "GrDrawContext.h"
+#include "GrDrawTarget.h"
 #include "GrPathRendering.h"
 
 class GrFixedClip;
@@ -20,6 +21,10 @@ struct GrUserStencilSettings;
     data members or virtual methods. */
 class GrDrawContextPriv {
 public:
+    gr_instanced::InstancedRendering* accessInstancedRendering() const {
+        return fDrawContext->getDrawTarget()->instancedRendering();
+    }
+
     void clearStencilClip(const SkIRect& rect, bool insideClip);
 
     void stencilRect(const GrFixedClip& clip,