Introduce bridge relayers pallet (#1513)

* introduce relayers pallet

* add MessageDeliveryAndDispatchPaymentAdapter

* plug in pallet into test runtimes

* tests prototype

* tests for the relayers pallet

* tests for payment adapter

* mint_reward_payment_procedure_actually_mints_tokens

* benchmarks

* remove irrelevant todo

* remove redundant clone

bridges/modules/relayers/src/benchmarking.rs

@@ -0,0 +1,40 @@
+// Copyright 2019-2021 Parity Technologies (UK) Ltd.
+// This file is part of Parity Bridges Common.
+
+// Parity Bridges Common is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// Parity Bridges Common is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with Parity Bridges Common.  If not, see <http://www.gnu.org/licenses/>.
+
+//! Benchmarks for the relayers Pallet.
+
+#![cfg(feature = "runtime-benchmarks")]
+
+use crate::*;
+
+use frame_benchmarking::{benchmarks, whitelisted_caller};
+use frame_system::RawOrigin;
+
+/// Reward amount that is (hopefully) is larger than existential deposit across all chains.
+const REWARD_AMOUNT: u32 = u32::MAX;
+
+benchmarks! {
+	// Benchmark `claim_rewards` call.
+	claim_rewards {
+		let relayer: T::AccountId = whitelisted_caller();
+		RelayerRewards::<T>::insert(&relayer, T::Reward::from(REWARD_AMOUNT));
+	}: _(RawOrigin::Signed(relayer))
+	verify {
+		// we can't check anything here, because `PaymentProcedure` is responsible for
+		// payment logic, so we assume that if call has succeeded, the procedure has
+		// also completed successfully
+	}
+}