Hi,
I know this is not an easy topic. I have a good policies collecting events for example inside HTTP communication on Google Mail through proxy. But, when it comes to the local DLP Agent based ability, when monitoring the HTTPS inside IE, it is weak. It can get some easy POST's (don't know for PUT's), but it is not able to get details from the complex async upload dialog of Google Drive. (Even, I think the SPDY is not supported in IE 8 - internal business requirement.)
I personally think, the HTTP network probe can do more and this may be missing from the local DLP Agent, unfortunately. I have tested it with this result.
Regards,
Pavel