Initial version of Call::decode dispatch. (#300)

* Initial version of call dispatch.

* cargo fmt --all

* Remove unused stuff.

* cargo fmt --all

* weight is part of msg + events

* should_fail_on_weight_mismatch

* plug into runtime

* cargo fmt --all

* fix benchmarks compilation?

* expected/actual values in events

* return actual weight from MessageDispatch::dispatch()

* MessageOrigin -> InstanceId + move bridge_account_id to bp-runtime

* fix benchmarks again

* cargo fmt --all

* clippy

Co-authored-by: Svyatoslav Nikolsky <svyatonik@gmail.com>

bridges/primitives/message-dispatch/src/lib.rs

@@ -0,0 +1,40 @@
+// Copyright 2019-2020 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/>.
+
+//! A common interface for all Bridge Message Dispatch modules.
+
+#![cfg_attr(not(feature = "std"), no_std)]
+#![warn(missing_docs)]
+
+use bp_runtime::InstanceId;
+
+/// Message dispatch weight.
+pub type Weight = u64;
+
+/// A generic trait to dispatch arbitrary messages delivered over the bridge.
+pub trait MessageDispatch<MessageId> {
+	/// A type of the message to be dispatched.
+	type Message: codec::Decode;
+
+	/// Dispatches the message internally.
+	///
+	/// `bridge` indicates instance of deployed bridge where the message came from.
+	///
+	/// `id` is a short unique if of the message.
+	///
+	/// Returns post-dispatch (actual) message weight.
+	fn dispatch(bridge: InstanceId, id: MessageId, message: Self::Message) -> Weight;
+}