Implement instanced rendering for simple shapes

src/gpu/gl/GrGLGpu.h

Index: src/gpu/gl/GrGLGpu.h
diff --git a/src/gpu/gl/GrGLGpu.h b/src/gpu/gl/GrGLGpu.h
index 57d076094cb666daceb19b014627c0771a56f2a6..a86a2f30a2127fc191e219579a4a1dc0e828970a 100644
--- a/src/gpu/gl/GrGLGpu.h
+++ b/src/gpu/gl/GrGLGpu.h
@@ -54,6 +54,8 @@ public:
         return static_cast<GrGLPathRendering*>(pathRendering());
     }
 
+    GrInstancedRendering* createInstancedRenderingIfSupported() override;
+
     void discard(GrRenderTarget*) override;
 
     // Used by GrGLProgram to configure OpenGL state.
@@ -568,6 +570,7 @@ private:
 
     typedef GrGpu INHERITED;
     friend class GrGLPathRendering; // For accessing setTextureUnit.
+    friend class GrGLInstancedRendering; // For accessing flushGLState.
 };
 
 #endif