Add test configs for instanced rendering

src/gpu/GrGpu.h

Index: src/gpu/GrGpu.h
diff --git a/src/gpu/GrGpu.h b/src/gpu/GrGpu.h
index 37427b5739ce9d1666150341be629edd78824401..393df1a9b650a4bccd2ac2718a65a0c6ddefb179 100644
--- a/src/gpu/GrGpu.h
+++ b/src/gpu/GrGpu.h
@@ -152,9 +152,7 @@ public:
     /**
      * Creates an instanced rendering object if it is supported on this platform.
      */
-    virtual gr_instanced::InstancedRendering* createInstancedRenderingIfSupported() {
-        return nullptr;
-    }
+    gr_instanced::InstancedRendering* createInstancedRendering();
 
     /**
      * Resolves MSAA.
@@ -537,6 +535,8 @@ private:
     virtual GrBuffer* onCreateBuffer(size_t size, GrBufferType intendedType, GrAccessPattern,
                                      const void* data) = 0;
 
+    virtual gr_instanced::InstancedRendering* onCreateInstancedRendering() = 0;
+
     virtual bool onMakeCopyForTextureParams(GrTexture* texture, const GrTextureParams&,
                                             GrTextureProducer::CopyParams*) const { return false; }