Add events to xDomain messengers (#61)

packages/contracts/contracts/optimistic-ethereum/OVM/bridge/OVM_BaseCrossDomainMessenger.sol

@@ -50,6 +50,8 @@ contract OVM_BaseCrossDomainMessenger is iOVM_BaseCrossDomainMessenger {
 
         messageNonce += 1;
         sentMessages[keccak256(xDomainCalldata)] = true;
+
+        emit SentMessage(xDomainCalldata);
     }
 
     /**********************

packages/contracts/contracts/optimistic-ethereum/OVM/bridge/OVM_L1CrossDomainMessenger.sol

@@ -78,8 +78,10 @@ contract OVM_L1CrossDomainMessenger is iOVM_L1CrossDomainMessenger, OVM_BaseCros
             "Provided message could not be verified."
         );
 
+        bytes32 xDomainCalldataHash = keccak256(xDomainCalldata);
+
         require(
-            successfulMessages[keccak256(xDomainCalldata)] == false,
+            successfulMessages[xDomainCalldataHash] == false,
             "Provided message has already been received."
         );
 
@@ -89,7 +91,8 @@ contract OVM_L1CrossDomainMessenger is iOVM_L1CrossDomainMessenger, OVM_BaseCros
         // Mark the message as received if the call was successful. Ensures that a message can be
         // relayed multiple times in the case that the call reverted.
         if (success == true) {
-            successfulMessages[keccak256(xDomainCalldata)] = true;
+            successfulMessages[xDomainCalldataHash] = true;
+            emit RelayedMessage(xDomainCalldataHash);
         }
 
         // Store an identifier that can be used to prove that the given message was relayed by some

packages/contracts/contracts/optimistic-ethereum/OVM/bridge/OVM_L2CrossDomainMessenger.sol

@@ -60,8 +60,10 @@ contract OVM_L2CrossDomainMessenger is iOVM_L2CrossDomainMessenger, OVM_BaseCros
             _messageNonce
         );
 
+        bytes32 xDomainCalldataHash = keccak256(xDomainCalldata);
+
         require(
-            successfulMessages[keccak256(xDomainCalldata)] == false,
+            successfulMessages[xDomainCalldataHash] == false,
             "Provided message has already been received."
         );
 
@@ -71,7 +73,8 @@ contract OVM_L2CrossDomainMessenger is iOVM_L2CrossDomainMessenger, OVM_BaseCros
         // Mark the message as received if the call was successful. Ensures that a message can be
         // relayed multiple times in the case that the call reverted.
         if (success == true) {
-            successfulMessages[keccak256(xDomainCalldata)] = true;
+            successfulMessages[xDomainCalldataHash] = true;
+            emit RelayedMessage(xDomainCalldataHash);
         }
 
         // Store an identifier that can be used to prove that the given message was relayed by some

packages/contracts/contracts/optimistic-ethereum/iOVM/bridge/iOVM_BaseCrossDomainMessenger.sol

@@ -6,6 +6,13 @@ pragma experimental ABIEncoderV2;
  * @title iOVM_BaseCrossDomainMessenger
  */
 interface iOVM_BaseCrossDomainMessenger {
+
+    /**********
+     * Events *
+     **********/
+    event SentMessage(bytes message);
+    event RelayedMessage(bytes32 msgHash);
+
     /**********************
      * Contract Variables *
      **********************/