Split out from  issue 724322 

Can you elaborate more on why we need URLLoaderStart? i.e. is it not sufficient that the C++ interface creates URLLoader implementations that are started?

My understanding is that URLLoader may comes from the network service or somewhere in the browser. It would convenient to have a consistent way to start it. For example, ThrottlingURLLoader controls whether/when to start a request. It is inconvenient if it has to know about the different ways of starting a request.

Can't we assume that whoever provides a URLLoader in the browser returns it started?

I think we could do that, too. Just trying to say that in that case, whoever needs to control when to start a request may need to either (1) know about the difference between URLLoaderFactory and the browser-side C++ interface; or (2) hide that difference behind another C++ interface.

And *not* adding URLLoader::Start avoids adding one more IPC, which is nice.

We have another example where we want to get a non-started loader, so having Start on URLLoader feels certainly handier / consistent.  We could try the other way too, let's see which way we like.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/d8b13e21c0c676d7f8e075236948983d09b42bbe

commit d8b13e21c0c676d7f8e075236948983d09b42bbe
Author: kinuko <kinuko@chromium.org>
Date: Wed Jun 07 06:59:26 2017

Get rid of URLLoaderFactory in browser-side case

BUG= 729503 

Review-Url: https://codereview.chromium.org/2919313004
Cr-Commit-Position: refs/heads/master@{#477568}

[modify] https://crrev.com/d8b13e21c0c676d7f8e075236948983d09b42bbe/content/browser/loader/navigation_url_loader_network_service.cc
[modify] https://crrev.com/d8b13e21c0c676d7f8e075236948983d09b42bbe/content/browser/loader/url_loader_request_handler.h
[modify] https://crrev.com/d8b13e21c0c676d7f8e075236948983d09b42bbe/content/browser/service_worker/service_worker_controllee_request_handler.cc
[modify] https://crrev.com/d8b13e21c0c676d7f8e075236948983d09b42bbe/content/browser/service_worker/service_worker_controllee_request_handler.h
[modify] https://crrev.com/d8b13e21c0c676d7f8e075236948983d09b42bbe/content/browser/service_worker/service_worker_request_handler.cc
[modify] https://crrev.com/d8b13e21c0c676d7f8e075236948983d09b42bbe/content/browser/service_worker/service_worker_request_handler.h
[modify] https://crrev.com/d8b13e21c0c676d7f8e075236948983d09b42bbe/content/browser/service_worker/service_worker_url_job_wrapper.cc
[modify] https://crrev.com/d8b13e21c0c676d7f8e075236948983d09b42bbe/content/browser/service_worker/service_worker_url_job_wrapper.h

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/acde73a7fa15b3877a342ddd8c5d71e97f070aa8

commit acde73a7fa15b3877a342ddd8c5d71e97f070aa8
Author: kinuko <kinuko@chromium.org>
Date: Thu Jun 08 04:41:50 2017

Use independent URLLoader in browser-side code

BUG= 729503 

Review-Url: https://codereview.chromium.org/2931623002
Cr-Commit-Position: refs/heads/master@{#477890}

[modify] https://crrev.com/acde73a7fa15b3877a342ddd8c5d71e97f070aa8/content/browser/loader/navigation_url_loader_network_service.cc
[modify] https://crrev.com/acde73a7fa15b3877a342ddd8c5d71e97f070aa8/content/browser/loader/navigation_url_loader_network_service.h
[modify] https://crrev.com/acde73a7fa15b3877a342ddd8c5d71e97f070aa8/content/browser/loader/url_loader_request_handler.h
[modify] https://crrev.com/acde73a7fa15b3877a342ddd8c5d71e97f070aa8/content/browser/service_worker/service_worker_url_job_wrapper.cc

Apologies, applied the wrong component in bulk.