You can know for sure that not only the Chinese patents and patent applications coming from the PCT Route are included in Google Patents because:
The Chinese document coverage in Google Patents includes patent documents from 1985 and 1990.
China became a PCT Contracting State in January 1994.
Only international applications with a filing date on or after ...
Wikipeadia says that google patents covers the following but I would not assume that the coverage is 100% complete in any dimension.
United States Patent and Trademark Office (USPTO),
European Patent Office (EPO),
China's National Intellectual Property Administration (CNIPA),
Japan Patent Office (JPO),
Korean Intellectual Property Office (KIPO),
Personally, I find problems with Google Patents not finding all the relevant patents when I search. It is, however handy for finding an individual patent quickly. I prefer The Lens which I find more full featured, especially if you register (free). Ultimately, if you want detailed file histories, there is no substitute for individual country databases like ...