Reland "Port policy::UploadJobImpl to network::SimpleURLLoader"

This reverts commit b624551f1c22ac5139c9ced011da1a15c2027b7c.

Reason for revert: Reverting this change broke the tree because of a patch that depends on it. Since the test is only flaky fixing the tree is better than causing more disturbance by reverting more changes.

Original change's description:
> Revert "Port policy::UploadJobImpl to network::SimpleURLLoader"
> 
> This reverts commit 581330a9f8fa0cd9b3b83def1611740a186a4881.
> 
> Reason for revert: SimpleURLLoaderTest.OnUploadProgressCallback/3 is flaky
> 
> Original change's description:
> > Port policy::UploadJobImpl to network::SimpleURLLoader
> > 
> > This change ports UploadJobImpl from net::URLFetcher to SimpleURLLoader.
> > 
> > Since this request does not make use of the response a new method has
> > been added to SimpleURLLoader, DownloadToNull. This download mode still
> > reads the response body from the network but does not save it anywhere.
> > This is useful for requests which upload data and would otherwise have
> > to specify an arbitrary |max_body_size|. A maximum may still be set if
> > the caller wants to limit the amount of data transferred over the
> > network.
> > 
> > Bug: 773295
> > Cq-Include-Trybots: luci.chromium.try:linux_mojo
> > Change-Id: Iee1fdc6f7406066ced8c91122e22cd51ddcb1c5f
> > Reviewed-on: https://chromium-review.googlesource.com/1161551
> > Commit-Queue: Reilly Grant <reillyg@chromium.org>
> > Reviewed-by: Matt Menke <mmenke@chromium.org>
> > Reviewed-by: Julian Pastarmov <pastarmovj@chromium.org>
> > Cr-Commit-Position: refs/heads/master@{#581060}
> 
> TBR=pastarmovj@chromium.org,reillyg@chromium.org,mmenke@chromium.org
> 
> Change-Id: Ica09c85a12861d35efbdfd9a882d137bac6b9e56
> No-Presubmit: true
> No-Tree-Checks: true
> No-Try: true
> Bug: 773295, 872023
> Cq-Include-Trybots: luci.chromium.try:linux_mojo
> Reviewed-on: https://chromium-review.googlesource.com/1166288
> Reviewed-by: Reilly Grant <reillyg@chromium.org>
> Commit-Queue: Reilly Grant <reillyg@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#581389}

TBR=pastarmovj@chromium.org,reillyg@chromium.org,mmenke@chromium.org

Change-Id: I793ab6c8c22c5bec97ef853f520dc506809970cb
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 773295, 872023
Cq-Include-Trybots: luci.chromium.try:linux_mojo
Reviewed-on: https://chromium-review.googlesource.com/1166301
Reviewed-by: Reilly Grant <reillyg@chromium.org>
Commit-Queue: Reilly Grant <reillyg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#581394}
8 files changed