How to use the @0x/contract-wrappers.ERC20TokenContract function in @0x/contract-wrappers

});

    // A small share is kept for the operator, note 1,000,000 represents all rebates
    // going to the operator
    const operatorSharePpm = new BigNumber(900000); // 90 %
    const stakingPoolReceipt = await stakingContract
        .createStakingPool(operatorSharePpm, true)
        .awaitTransactionSuccessAsync({
            from: maker,
        });
    const createStakingPoolLog = stakingPoolReceipt.logs[0];
    const poolId = (createStakingPoolLog as any).args.poolId;
    await printUtils.awaitTransactionMinedSpinnerAsync(`Create Pool ${poolId}`, stakingPoolReceipt.transactionHash);

    // Approve the ZRX token for Staking using the ERC20Proxy
    const zrxTokenContract = new ERC20TokenContract(zrxTokenAddress, providerEngine, { from: maker });
    await zrxTokenContract
        .approve(contractWrappers.contractAddresses.erc20Proxy, UNLIMITED_ALLOWANCE_IN_BASE_UNITS)
        .sendTransactionAsync();

    // Stake 1000 ZRX
    const stakeAmount = Web3Wrapper.toBaseUnitAmount(new BigNumber(100), DECIMALS);
    // Transfer the ZRX to the Staking Contract
    txHash = await stakingContract.stake(stakeAmount).sendTransactionAsync({ from: maker });
    await printUtils.awaitTransactionMinedSpinnerAsync('Stake ZRX', txHash);
    // Move the staked ZRX to delegate the Staking Pool
    txHash = await stakingContract
        .moveStake(
            { status: StakeStatus.Undelegated, poolId: NIL_POOL_ID },
            { status: StakeStatus.Delegated, poolId },
            stakeAmount,
        )

public async getZrxBalanceAsync(owner: string): Promise {
        utils.assert(this._contractWrappers !== undefined, 'ContractWrappers must be instantiated.');
        const contractAddresses = getContractAddressesForNetworkOrThrow(this.networkId);
        const tokenAddress: string = contractAddresses.zrxToken;
        const erc20Token = new ERC20TokenContract(tokenAddress, this._contractWrappers.getProvider());
        try {
            const amount = await erc20Token.balanceOf.callAsync(owner);
            return amount;
        } catch (error) {
            return ZERO;
        }
    }
    private async _onConnectWalletClickAsync(): Promise {