skipWhile(predicate) {
        let seq = this._iterable;
        return Seq.fromGenerator(function*() {
            let matched = true;
            for (let e of seq) {
                matched = matched && predicate(e);
                if (!matched) {
                    yield e;
                }
            }
        });
    }
Returns a sequence with the same items, except items at the start of the sequence are skipped until an item
doesn't satisfy the given predicate.
@param {!function(T) : !boolean} predicate
@returns {!Seq.<T>}
@template T