Fix warning in Fuchsia build

Change-Id: I3f148af37e29eca3390ca1cff3ec96a913b8fac4
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/257038
Commit-Queue: Jim Van Verth <jvanverth@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
Auto-Submit: Jim Van Verth <jvanverth@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>

src/gpu/GrDDLContext.cpp

@@ -15,7 +15,7 @@
  * The DDL Context is the one in effect during DDL Recording. It isn't backed by a GrGPU and
  * cannot allocate any GPU resources.
  */
-class GrDDLContext : public GrContext {
+class GrDDLContext final : public GrContext {
 public:
     GrDDLContext(sk_sp<GrContextThreadSafeProxy> proxy)
             : INHERITED(proxy->backend(), proxy->priv().options(), proxy->priv().contextID()) {