Get the Promise of an account on Ethereum Mist.

mistRequestAccountPromise.js

if (typeof(mist) !== "undefined") {
    mist.requestAccountPromise = function () {
        return new Promise (function (resolve, reject) {
            mist.requestAccount(function(e, account) {
                if(e != null) {
                    reject(e);
                } else {
                    resolve(account);
                }
            });
        });
    };
}