Add missing GRPC_OVERRIDE, NFC

src/cpp/client/insecure_credentials.cc

@@ -54,7 +54,7 @@ class InsecureCredentialsImpl GRPC_FINAL : public Credentials {
         target, grpc_channel_create(target.c_str(), &channel_args)));
   }
 
-  SecureCredentials* AsSecureCredentials() { return nullptr; }
+  SecureCredentials* AsSecureCredentials() GRPC_OVERRIDE { return nullptr; }
 };
 }  // namespace
 

src/cpp/client/secure_credentials.cc

@@ -59,7 +59,7 @@ class SecureCredentials GRPC_FINAL : public Credentials {
         grpc_secure_channel_create(c_creds_, target.c_str(), &channel_args)));
   }
 
-  SecureCredentials* AsSecureCredentials() { return this; }
+  SecureCredentials* AsSecureCredentials() GRPC_OVERRIDE { return this; }
 
  private:
   grpc_credentials* const c_creds_;