Add utilities for CrossChain messaging (#3183)

Co-authored-by: Francisco Giordano <frangio.1@gmail.com>

contracts/vendor/arbitrum/IBridge.sol

@@ -0,0 +1,65 @@
+// SPDX-License-Identifier: Apache-2.0
+
+/*
+ * Copyright 2021, Offchain Labs, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+pragma solidity ^0.8.0;
+
+interface IBridge {
+    event MessageDelivered(
+        uint256 indexed messageIndex,
+        bytes32 indexed beforeInboxAcc,
+        address inbox,
+        uint8 kind,
+        address sender,
+        bytes32 messageDataHash
+    );
+
+    event BridgeCallTriggered(address indexed outbox, address indexed destAddr, uint256 amount, bytes data);
+
+    event InboxToggle(address indexed inbox, bool enabled);
+
+    event OutboxToggle(address indexed outbox, bool enabled);
+
+    function deliverMessageToInbox(
+        uint8 kind,
+        address sender,
+        bytes32 messageDataHash
+    ) external payable returns (uint256);
+
+    function executeCall(
+        address destAddr,
+        uint256 amount,
+        bytes calldata data
+    ) external returns (bool success, bytes memory returnData);
+
+    // These are only callable by the admin
+    function setInbox(address inbox, bool enabled) external;
+
+    function setOutbox(address inbox, bool enabled) external;
+
+    // View functions
+
+    function activeOutbox() external view returns (address);
+
+    function allowedInboxes(address inbox) external view returns (bool);
+
+    function allowedOutboxes(address outbox) external view returns (bool);
+
+    function inboxAccs(uint256 index) external view returns (bytes32);
+
+    function messageCount() external view returns (uint256);
+}