function parsePayload(error, computedPayload)
        {
            if (error || !computedPayload)
                return null;
            var result = new Map();
            for (var property of computedPayload)
                result.set(property.name, property.value);
            return result;
        }
@param {?Protocol.Error} error
@param {!Array.<!CSSAgent.CSSComputedStyleProperty>} computedPayload
@return {?Map.<string, string>}