WIP - Have Escrow forward all gas on withdraw.

contracts/mocks/FallbackGasReporter.sol

@@ -0,0 +1,9 @@
+pragma solidity ^0.5.2;
+
+contract FallbackGasReporter {
+    event RemainingGas(uint256 amount);
+
+    function () external payable {
+        emit RemainingGas(gasleft());
+    }
+}

contracts/payment/escrow/Escrow.sol

@@ -1,6 +1,7 @@
 pragma solidity ^0.5.2;
 
 import "../../math/SafeMath.sol";
+import "../../utils/Address.sol";
 import "../../ownership/Secondary.sol";
 
  /**
@@ -17,6 +18,7 @@ import "../../ownership/Secondary.sol";
   */
 contract Escrow is Secondary {
     using SafeMath for uint256;
+    using Address for address payable;
 
     event Deposited(address indexed payee, uint256 weiAmount);
     event Withdrawn(address indexed payee, uint256 weiAmount);
@@ -47,7 +49,7 @@ contract Escrow is Secondary {
 
         _deposits[payee] = 0;
 
-        payee.transfer(payment);
+        payee.transferWithGas(payment);
 
         emit Withdrawn(payee, payment);
     }

contracts/payment/escrow/RefundEscrow.sol

@@ -1,6 +1,7 @@
 pragma solidity ^0.5.2;
 
 import "./ConditionalEscrow.sol";
+import "../../utils/Address.sol";
 
 /**
  * @title RefundEscrow
@@ -14,6 +15,8 @@ import "./ConditionalEscrow.sol";
  * RefundableCrowdsale contract for an example of RefundEscrow’s use.
  */
 contract RefundEscrow is ConditionalEscrow {
+    using Address for address payable;
+
     enum State { Active, Refunding, Closed }
 
     event RefundsClosed();
@@ -79,7 +82,7 @@ contract RefundEscrow is ConditionalEscrow {
      */
     function beneficiaryWithdraw() public {
         require(_state == State.Closed);
-        _beneficiary.transfer(address(this).balance);
+        _beneficiary.transferWithGas(address(this).balance);
     }
 
     /**

contracts/utils/Address.sol

@@ -23,4 +23,9 @@ library Address {
         assembly { size := extcodesize(account) }
         return size > 0;
     }
+
+    function transferWithGas(address payable account, uint256 amount) internal {
+        (bool success,) = account.call.value(amount)(""); // solhint-disable-line avoid-call-value
+        require(success);
+    }
 }

test/payment/escrow/Escrow.behavior.js

@@ -1,5 +1,7 @@
 const { balance, ether, expectEvent, shouldFail } = require('openzeppelin-test-helpers');
 
+const FallbackGasReporter = artifacts.require('FallbackGasReporter');
+
 function shouldBehaveLikeEscrow (primary, [payee1, payee2]) {
   const amount = ether('42');
 
@@ -67,6 +69,16 @@ function shouldBehaveLikeEscrow (primary, [payee1, payee2]) {
         await this.escrow.withdraw(payee1, { from: primary });
       });
 
+      it('forwards all gas', async function () {
+        const gasReporter = await FallbackGasReporter.new();
+
+        const { tx } = await this.escrow.withdraw(gasReporter.address, { from: primary });
+        const event = await expectEvent.inTransaction(tx, FallbackGasReporter, 'RemainingGas');
+
+        // This doesn't really test that _all_ gas is forwarded, but it does test that `transfer` wasn't used
+        event.args.amount.should.be.bignumber.greaterThan('2300');
+      });
+
       it('only the primary account can withdraw', async function () {
         await shouldFail.reverting(this.escrow.withdraw(payee1, { from: payee1 }));
       });