It seems that there is no link to the web function, but the Windows HTMLHelp ZIP file (.CFM) file (LoadRunner 9.10 VuGen API API link) can be downloaded here :
I found this by searching the HP Product Guide with the following data (free registration required):
Product: LoadRunner
Product version: 9.10
Operating system: Windows
9.50, ...
: .CFM , "" "", " -" HTMLHelp.