The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/7b485fc777e2aedf7031f8dd62ade73f8becd2ee

commit 7b485fc777e2aedf7031f8dd62ade73f8becd2ee
Author: Marijn Kruisselbrink <mek@chromium.org>
Date: Thu Mar 22 23:45:20 2018

Add usecounter for DownloadToFile usage in PPAPI.

Bug:  823522 
Change-Id: I1a01575324982def3c1f085898d15e5db9cd7f01
Reviewed-on: https://chromium-review.googlesource.com/969712
Commit-Queue: Marijn Kruisselbrink <mek@chromium.org>
Reviewed-by: Rick Byers <rbyers@chromium.org>
Reviewed-by: Raymes Khoury <raymes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#545290}
[modify] https://crrev.com/7b485fc777e2aedf7031f8dd62ade73f8becd2ee/content/renderer/pepper/url_request_info_util.cc
[modify] https://crrev.com/7b485fc777e2aedf7031f8dd62ade73f8becd2ee/third_party/WebKit/public/platform/web_feature.mojom
[modify] https://crrev.com/7b485fc777e2aedf7031f8dd62ade73f8becd2ee/tools/metrics/histograms/enums.xml

here are the stats that Marijn added https://www.chromestatus.com/metrics/feature/timeline/popularity/2396

(paraphrasing from 791702) since the use counter is showing pretty much zero usage, my proposal would be to either:
- make the PPAPI exposed API for DownloadToFile fail in M68, and actually get rid of the implementation in M69
- or just get rid of everything now

I'd prefer the first option, in the event that there are unanticipated usages.

this will not block canary.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/23efe422cf0cda9a08f542738e1b73b9b170df08

commit 23efe422cf0cda9a08f542738e1b73b9b170df08
Author: Marijn Kruisselbrink <mek@chromium.org>
Date: Thu May 24 23:17:42 2018

Disable the DownloadToFile API in PPAPI.

The use counter is showing pretty much zero usage of this API, so as a
first step towards removing the implementation of DownloadToFile, this
changes the exposed API to always fail when attempting to use it.

Bug:  823522 
Change-Id: Ic82280d3d203684467fa4845b255cff9a02e1e12
Reviewed-on: https://chromium-review.googlesource.com/1062705
Reviewed-by: John Abd-El-Malek <jam@chromium.org>
Reviewed-by: Bill Budge <bbudge@chromium.org>
Reviewed-by: Mark Seaborn <mseaborn@chromium.org>
Reviewed-by: Raymes Khoury <raymes@chromium.org>
Commit-Queue: Marijn Kruisselbrink <mek@chromium.org>
Cr-Commit-Position: refs/heads/master@{#561682}
[modify] https://crrev.com/23efe422cf0cda9a08f542738e1b73b9b170df08/chrome/test/ppapi/ppapi_test.cc
[modify] https://crrev.com/23efe422cf0cda9a08f542738e1b73b9b170df08/chrome/test/ppapi/ppapi_test.h
[modify] https://crrev.com/23efe422cf0cda9a08f542738e1b73b9b170df08/components/nacl/browser/nacl_process_host.cc
[modify] https://crrev.com/23efe422cf0cda9a08f542738e1b73b9b170df08/content/renderer/pepper/pepper_url_request_unittest.cc
[modify] https://crrev.com/23efe422cf0cda9a08f542738e1b73b9b170df08/ppapi/api/ppb_url_request_info.idl
[modify] https://crrev.com/23efe422cf0cda9a08f542738e1b73b9b170df08/ppapi/api/ppb_url_response_info.idl
[modify] https://crrev.com/23efe422cf0cda9a08f542738e1b73b9b170df08/ppapi/c/ppb_url_request_info.h
[modify] https://crrev.com/23efe422cf0cda9a08f542738e1b73b9b170df08/ppapi/c/ppb_url_response_info.h
[modify] https://crrev.com/23efe422cf0cda9a08f542738e1b73b9b170df08/ppapi/cpp/url_request_info.h
[modify] https://crrev.com/23efe422cf0cda9a08f542738e1b73b9b170df08/ppapi/cpp/url_response_info.h
[modify] https://crrev.com/23efe422cf0cda9a08f542738e1b73b9b170df08/ppapi/nacl_irt/ppapi_dispatcher.cc
[modify] https://crrev.com/23efe422cf0cda9a08f542738e1b73b9b170df08/ppapi/proxy/url_loader_resource.cc
[modify] https://crrev.com/23efe422cf0cda9a08f542738e1b73b9b170df08/ppapi/proxy/url_request_info_resource.cc
[modify] https://crrev.com/23efe422cf0cda9a08f542738e1b73b9b170df08/ppapi/shared_impl/BUILD.gn
[add] https://crrev.com/23efe422cf0cda9a08f542738e1b73b9b170df08/ppapi/shared_impl/ppapi_features.cc
[add] https://crrev.com/23efe422cf0cda9a08f542738e1b73b9b170df08/ppapi/shared_impl/ppapi_features.h
[modify] https://crrev.com/23efe422cf0cda9a08f542738e1b73b9b170df08/ppapi/tests/test_file_ref.cc
[modify] https://crrev.com/23efe422cf0cda9a08f542738e1b73b9b170df08/ppapi/tests/test_url_loader.cc
[modify] https://crrev.com/23efe422cf0cda9a08f542738e1b73b9b170df08/ppapi/tests/test_url_request.cc

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/c81d89c760ac79bf17157fd33012704063f77d58

commit c81d89c760ac79bf17157fd33012704063f77d58
Author: Marijn Kruisselbrink <mek@chromium.org>
Date: Wed May 30 19:13:37 2018

[PPAPI] Make FileRef tests no longer depend on StreamToFile.

This moves TestSelectFileDialogFactory out of ppapi_filechooser_browsertest.cc
to its own separate file, so the FileRef tests can also use the same select
file dialog implementation to get access to an "external" file ref.

Bug:  823522 ,  791702 
Change-Id: Ic68f15fe52e4cac78542ed01fe2ac76546e7fb78
Reviewed-on: https://chromium-review.googlesource.com/1065050
Reviewed-by: Bill Budge <bbudge@chromium.org>
Commit-Queue: Marijn Kruisselbrink <mek@chromium.org>
Cr-Commit-Position: refs/heads/master@{#562949}
[modify] https://crrev.com/c81d89c760ac79bf17157fd33012704063f77d58/chrome/test/BUILD.gn
[modify] https://crrev.com/c81d89c760ac79bf17157fd33012704063f77d58/chrome/test/ppapi/ppapi_browsertest.cc
[modify] https://crrev.com/c81d89c760ac79bf17157fd33012704063f77d58/chrome/test/ppapi/ppapi_filechooser_browsertest.cc
[modify] https://crrev.com/c81d89c760ac79bf17157fd33012704063f77d58/chrome/test/ppapi/ppapi_test.cc
[add] https://crrev.com/c81d89c760ac79bf17157fd33012704063f77d58/chrome/test/ppapi/ppapi_test_select_file_dialog_factory.cc
[add] https://crrev.com/c81d89c760ac79bf17157fd33012704063f77d58/chrome/test/ppapi/ppapi_test_select_file_dialog_factory.h
[modify] https://crrev.com/c81d89c760ac79bf17157fd33012704063f77d58/ppapi/tests/test_file_ref.cc

Only thing remaining is actualy removing the implementation of DownloadToFile, and that is tracked in 791702