Add gas burn to enqueue

packages/contracts/contracts/optimistic-ethereum/OVM/queue/OVM_L1ToL2TransactionQueue.sol

@@ -17,6 +17,13 @@ import { OVM_BaseQueue } from "./OVM_BaseQueue.sol";
  */
 contract OVM_L1ToL2TransactionQueue is iOVM_L1ToL2TransactionQueue, OVM_BaseQueue, Lib_AddressResolver {
 
+
+    /*********************************
+     * Contract Variables: Constants *
+     ********************************/
+
+    uint constant public L2_GAS_DISCOUNT_DIVISOR = 10;
+
     /*******************************************
      * Contract Variables: Contract References *
      *******************************************/
@@ -58,6 +65,14 @@ contract OVM_L1ToL2TransactionQueue is iOVM_L1ToL2TransactionQueue, OVM_BaseQueu
         override
         public
     {
+        require(_gasLimit >= 20000, "Gas limit too low.");
+        uint gasToBurn = _gasLimit / L2_GAS_DISCOUNT_DIVISOR;
+        uint startingGas = gasleft();
+        uint i;
+        while(startingGas - gasleft() > gasToBurn) {
+            i++; // TODO: Replace this dumb work with minting gas token.
+        }
+
         Lib_OVMCodec.QueueElement memory element = Lib_OVMCodec.QueueElement({
             timestamp: block.timestamp,
             batchRoot: keccak256(abi.encodePacked(

packages/contracts/test/contracts/OVM/queue/OVM_L1ToL2TransactionQueue.spec.ts

@@ -31,7 +31,7 @@ const makeQueueElements = (count: number): any => {
   return [...Array(count)].map((el, idx) => {
     return {
       target: NON_ZERO_ADDRESS,
-      gasLimit: idx,
+      gasLimit: (idx + 1) * 20000,
       data: DUMMY_BYTES32[0],
     }
   })