Not actually actively working on this...

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/a780469e2f2de600512c592c36041002dd697a33

commit a780469e2f2de600512c592c36041002dd697a33
Author: Marijn Kruisselbrink <mek@chromium.org>
Date: Thu Aug 09 04:59:33 2018

[FileSystem]: Rewrite FileWriterDelegate using BlobReader rather than URLRequest.

Not perfect, since this really should be going through the mojo interface
for dealing with blobs, but a lot better than going through blob URLs.

Tbr: reillyg@chromium.org
Bug:  859594 ,  868462 , 804546
Change-Id: Ifd7cd11b7bf4432eff41bdef00edd079d31e49c6
Reviewed-on: https://chromium-review.googlesource.com/1164523
Commit-Queue: Marijn Kruisselbrink <mek@chromium.org>
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Reviewed-by: Daniel Murphy <dmurph@chromium.org>
Cr-Commit-Position: refs/heads/master@{#581790}
[modify] https://crrev.com/a780469e2f2de600512c592c36041002dd697a33/chrome/browser/extensions/app_data_migrator_unittest.cc
[modify] https://crrev.com/a780469e2f2de600512c592c36041002dd697a33/chrome/browser/sync_file_system/local/canned_syncable_file_system.cc
[modify] https://crrev.com/a780469e2f2de600512c592c36041002dd697a33/chrome/browser/sync_file_system/local/canned_syncable_file_system.h
[modify] https://crrev.com/a780469e2f2de600512c592c36041002dd697a33/chrome/browser/sync_file_system/local/local_file_change_tracker_unittest.cc
[modify] https://crrev.com/a780469e2f2de600512c592c36041002dd697a33/chrome/browser/sync_file_system/local/syncable_file_operation_runner_unittest.cc
[modify] https://crrev.com/a780469e2f2de600512c592c36041002dd697a33/chrome/browser/sync_file_system/local/syncable_file_system_operation.cc
[modify] https://crrev.com/a780469e2f2de600512c592c36041002dd697a33/chrome/browser/sync_file_system/local/syncable_file_system_operation.h
[modify] https://crrev.com/a780469e2f2de600512c592c36041002dd697a33/content/browser/fileapi/fileapi_message_filter.cc
[modify] https://crrev.com/a780469e2f2de600512c592c36041002dd697a33/content/browser/fileapi/fileapi_message_filter.h
[modify] https://crrev.com/a780469e2f2de600512c592c36041002dd697a33/content/browser/fileapi/fileapi_message_filter_unittest.cc
[modify] https://crrev.com/a780469e2f2de600512c592c36041002dd697a33/content/browser/indexed_db/database_impl.cc
[modify] https://crrev.com/a780469e2f2de600512c592c36041002dd697a33/content/browser/indexed_db/indexed_db_backing_store.cc
[modify] https://crrev.com/a780469e2f2de600512c592c36041002dd697a33/content/browser/indexed_db/indexed_db_backing_store.h
[modify] https://crrev.com/a780469e2f2de600512c592c36041002dd697a33/content/browser/indexed_db/indexed_db_backing_store_unittest.cc
[modify] https://crrev.com/a780469e2f2de600512c592c36041002dd697a33/content/browser/indexed_db/indexed_db_blob_info.cc
[modify] https://crrev.com/a780469e2f2de600512c592c36041002dd697a33/content/browser/indexed_db/indexed_db_blob_info.h
[modify] https://crrev.com/a780469e2f2de600512c592c36041002dd697a33/content/browser/indexed_db/indexed_db_callbacks.cc
[modify] https://crrev.com/a780469e2f2de600512c592c36041002dd697a33/content/browser/indexed_db/indexed_db_database.cc
[modify] https://crrev.com/a780469e2f2de600512c592c36041002dd697a33/content/browser/indexed_db/indexed_db_database.h
[modify] https://crrev.com/a780469e2f2de600512c592c36041002dd697a33/content/browser/indexed_db/indexed_db_database_unittest.cc
[modify] https://crrev.com/a780469e2f2de600512c592c36041002dd697a33/content/browser/indexed_db/indexed_db_fake_backing_store.cc
[modify] https://crrev.com/a780469e2f2de600512c592c36041002dd697a33/content/browser/indexed_db/indexed_db_fake_backing_store.h
[modify] https://crrev.com/a780469e2f2de600512c592c36041002dd697a33/content/browser/renderer_host/render_process_host_impl.cc
[modify] https://crrev.com/a780469e2f2de600512c592c36041002dd697a33/storage/browser/fileapi/file_system_operation.h
[modify] https://crrev.com/a780469e2f2de600512c592c36041002dd697a33/storage/browser/fileapi/file_system_operation_impl.cc
[modify] https://crrev.com/a780469e2f2de600512c592c36041002dd697a33/storage/browser/fileapi/file_system_operation_impl.h
[modify] https://crrev.com/a780469e2f2de600512c592c36041002dd697a33/storage/browser/fileapi/file_system_operation_impl_write_unittest.cc
[modify] https://crrev.com/a780469e2f2de600512c592c36041002dd697a33/storage/browser/fileapi/file_system_operation_runner.cc
[modify] https://crrev.com/a780469e2f2de600512c592c36041002dd697a33/storage/browser/fileapi/file_system_operation_runner.h
[modify] https://crrev.com/a780469e2f2de600512c592c36041002dd697a33/storage/browser/fileapi/file_writer_delegate.cc
[modify] https://crrev.com/a780469e2f2de600512c592c36041002dd697a33/storage/browser/fileapi/file_writer_delegate.h
[modify] https://crrev.com/a780469e2f2de600512c592c36041002dd697a33/storage/browser/fileapi/file_writer_delegate_unittest.cc

That I believe leaves just one usage of CreateBlobRequest, in ServiceWorkerBlobReader. And that code should get deleted after SW s13n ships, so marking this bug as blocked on shipping SW S13n.