Introduce WebServiceWorkerNetworkProvider::GetProviderID() and stop static casting

content/renderer/service_worker/service_worker_context_client.cc

Index: content/renderer/service_worker/service_worker_context_client.cc
diff --git a/content/renderer/service_worker/service_worker_context_client.cc b/content/renderer/service_worker/service_worker_context_client.cc
index f98915ffd22c38cca63e8e2a1c4eeea588c77ecd..f181da5c2618be053c1e67c56ed03a0157a5f21a 100644
--- a/content/renderer/service_worker/service_worker_context_client.cc
+++ b/content/renderer/service_worker/service_worker_context_client.cc
@@ -103,6 +103,8 @@ class WebServiceWorkerNetworkProviderImpl
     request.SetExtraData(extra_data.release());
   }
 
+  int GetProviderID() const override { return provider_->provider_id(); }
+
  private:
   std::unique_ptr<ServiceWorkerNetworkProvider> provider_;
 };