'Collect all the different params we need for the URL.  Collecting
all params as a dict before converting to a URL makes testing easier.'

def _Params(self, chart):

    chart = chart.GetFormattedChart()
    params = {}
    def Add(new_params):
        params.update(util.ShortenParameterNames(new_params))
    for formatter in self.formatters:
        Add(formatter(chart))
    for key in params:
        params[key] = str(params[key])
    return params
