Implement instanced rendering for simple shapes

src/gpu/GrGpu.h

Index: src/gpu/GrGpu.h
diff --git a/src/gpu/GrGpu.h b/src/gpu/GrGpu.h
index 883b7ee98a91a1ff812c8be9f6c33464dfd6f021..c9f960c5b5bd9486ef71e3fe9f78f1c2ace009af 100644
--- a/src/gpu/GrGpu.h
+++ b/src/gpu/GrGpu.h
@@ -33,6 +33,7 @@ class GrPathRendering;
 class GrPipeline;
 class GrPrimitiveProcessor;
 class GrRenderTarget;
+class GrInstancedRendering;
 class GrStencilAttachment;
 class GrSurface;
 class GrTexture;
@@ -146,6 +147,11 @@ public:
                            const void* data = nullptr);
 
     /**
+     * Creates an instanced rendering object if it is supported on this platform.
+     */
+    virtual GrInstancedRendering* createInstancedRenderingIfSupported() { return nullptr; }
+
+    /**
      * Resolves MSAA.
      */
     void resolveRenderTarget(GrRenderTarget* target);