UserAgent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/71.0.3578.98 Safari/537.36

Steps to reproduce the problem:
1. open dev tools
2. attempt sign in at https://accounts.google.com
3. export network traffic as HAR-with-content
4. open HAR in text editor

What is the expected behavior?
`entry.request.bodySize` should be...

"Size of the request body (POST data payload) in bytes. Set to -1 if the info is not available."

(http://www.softwareishard.com/blog/har-12-spec/#request)

Maybe there needs to be some thought as to how to represent the request bodySize, as for a response, the `entry.response.bodySize` is represented as -1 with a new field `entry.response._transferredSize` representing the actual size of the response data sent over-the-wire.

Tools like HAR Viewer cannot represent request bodies accurately without this information.

What went wrong?
`entry.request.bodySize` is 0, instead of the size of the request body.

Did this work before? N/A 

Chrome version: 71.0.3578.98  Channel: stable
OS Version: 10.0
Flash Version: