About Web Page downloads

My basic requirement is I need to find the total time an android phone takes to download a webpage along with its DOM elements like images and other links regardless of the network.
How can we know that a webpage is completely downloaded? Browser after launching that page also continues to download other pages right?
Particularly in mobile phones how it is calculted.
WebPageTest comes up with a waterfall model to show this.
How this is calculated?

Moved this out of the WPT Monitor section…

Are you building software, just doing testing or measuring data from the field?

On Android WebPagetest uses the Blaze Agents where are custom applications that host a Web View. The application gets notifications when the page has loaded so it is pretty trivial to measure the overall time. The individual requests for the waterfall are captured through a tcpdump.

If you can step up to the Chrome browser on Android then you get much better features.

The browser itself supports the W3C navigation timing API so javascript on the page can query for all sorts of page performance information.

Additionally, Chrome for android supports remote debugging useing the dev tools on an attached desktop browser so you can get all of the timing remotely.