Page size is for paging and specifies the maximum number of returned rows.
Page size should be >= 0. A query returns the default of 1,000 rows.
The Analytics Core Reporting API returns a maximum of 100,000 rows per
request, no matter how many you ask for. It can also return fewer rows
than requested, if there aren't as many dimension segments as you expect.
For instance, there are fewer than 300 possible values for `ga:country`,
so when segmenting only by country, you can't get more than 300 rows,
even if you set `pageSize` to a higher value.