Chrome doesn't know how many bytes were required to be transferred over the network in order to load a web page, but should. This sort of accounting requires plumbing data use information in URLRequest objects in the network stack to page-level global state.

Note, as a result of out of process iframes, the Page object in Blink, which used to be a good place for page-global state, has moved to FrameHost, but it will eventually move to the browser process. 

When reporting page size, we should be clear about what is not included. Cases to consider include but are not limited to:
- service worker and app cache
- prerendering
- popups
- XHR
- video
- automatic navigations