Mark the leaf classes of GrOp final.

Change-Id: Ie8acbca972ce8628fc0a2a216a62c34c2a91059a
Reviewed-on: https://skia-review.googlesource.com/5927
Commit-Queue: Herb Derby <herb@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
diff --git a/src/gpu/instanced/GLInstancedRendering.cpp b/src/gpu/instanced/GLInstancedRendering.cpp
index d680189..b61b701 100644
--- a/src/gpu/instanced/GLInstancedRendering.cpp
+++ b/src/gpu/instanced/GLInstancedRendering.cpp
@@ -15,7 +15,7 @@
 
 namespace gr_instanced {
 
-class GLInstancedRendering::GLBatch : public InstancedRendering::Batch {
+class GLInstancedRendering::GLBatch final : public InstancedRendering::Batch {
 public:
     DEFINE_OP_CLASS_ID