Start a tick request that has the reqId associated with the contract.
        Return the ticker.

def startTicker(self, reqId, contract, tickType):
        """
        Start a tick request that has the reqId associated with the contract.
        Return the ticker.
        """
        ticker = self.tickers.get(id(contract))
        if not ticker:
            ticker = Ticker(
                contract=contract, ticks=[], tickByTicks=[],
                domBids=[], domAsks=[], domTicks=[])
            self.tickers[id(contract)] = ticker
        self.reqId2Ticker[reqId] = ticker
        self._reqId2Contract[reqId] = contract
        self.ticker2ReqId[tickType][ticker] = reqId
        return ticker