Tried to make some attempts, and still having one test failure in downloads API... just leaving the link here so that anyone interested in can take over (as it's p3...):

https://codereview.chromium.org/2940553003/

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/2ce3d229d5b4361e6c7d3f2f9e8aca8406620356

commit 2ce3d229d5b4361e6c7d3f2f9e8aca8406620356
Author: Emi Morikawa <emim@google.com>
Date: Fri Aug 25 11:29:20 2017

Add more ServiceWorkerURLLoaderJob tests: NonExistentBlobUUIDResponse.

Bug:  748416 ,  732750 
Change-Id: Ie14a3a3cb6f445d83ed054d80e241abfd3975b3f
Reviewed-on: https://chromium-review.googlesource.com/635064
Commit-Queue: Emi Morikawa <emim@google.com>
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Reviewed-by: Matt Falkenhagen <falken@chromium.org>
Cr-Commit-Position: refs/heads/master@{#497376}
[modify] https://crrev.com/2ce3d229d5b4361e6c7d3f2f9e8aca8406620356/content/browser/service_worker/service_worker_url_loader_job_unittest.cc

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/1e4e770ec53ab865cc8a0e85d9894f056cf8cc30

commit 1e4e770ec53ab865cc8a0e85d9894f056cf8cc30
Author: Daniel Murphy <dmurph@chromium.org>
Date: Mon Dec 18 09:26:15 2017

S13nServiceWorker: Use MojoBlob directly.

Adapted from falken@'s patch here:
https://chromium-review.googlesource.com/c/chromium/src/+/822019

Bug:  794104 ,  732750 
Cq-Include-Trybots: master.tryserver.chromium.linux:linux_mojo
Change-Id: If3e05ec30abb929794451c0fac7d141f416ebd2a
Reviewed-on: https://chromium-review.googlesource.com/823374
Commit-Queue: Daniel Murphy <dmurph@chromium.org>
Reviewed-by: Matt Falkenhagen <falken@chromium.org>
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Cr-Commit-Position: refs/heads/master@{#524666}
[modify] https://crrev.com/1e4e770ec53ab865cc8a0e85d9894f056cf8cc30/content/browser/service_worker/service_worker_controllee_request_handler.cc
[modify] https://crrev.com/1e4e770ec53ab865cc8a0e85d9894f056cf8cc30/content/browser/service_worker/service_worker_url_loader_job.cc
[modify] https://crrev.com/1e4e770ec53ab865cc8a0e85d9894f056cf8cc30/content/browser/service_worker/service_worker_url_loader_job.h
[modify] https://crrev.com/1e4e770ec53ab865cc8a0e85d9894f056cf8cc30/content/browser/service_worker/service_worker_url_loader_job_unittest.cc
[modify] https://crrev.com/1e4e770ec53ab865cc8a0e85d9894f056cf8cc30/content/common/service_worker/service_worker_loader_helpers.cc
[modify] https://crrev.com/1e4e770ec53ab865cc8a0e85d9894f056cf8cc30/content/common/service_worker/service_worker_loader_helpers.h
[modify] https://crrev.com/1e4e770ec53ab865cc8a0e85d9894f056cf8cc30/content/common/service_worker/service_worker_utils.cc
[modify] https://crrev.com/1e4e770ec53ab865cc8a0e85d9894f056cf8cc30/content/common/service_worker/service_worker_utils.h
[modify] https://crrev.com/1e4e770ec53ab865cc8a0e85d9894f056cf8cc30/content/renderer/service_worker/service_worker_provider_context.cc
[modify] https://crrev.com/1e4e770ec53ab865cc8a0e85d9894f056cf8cc30/content/renderer/service_worker/service_worker_subresource_loader.cc
[modify] https://crrev.com/1e4e770ec53ab865cc8a0e85d9894f056cf8cc30/content/renderer/service_worker/service_worker_subresource_loader.h
[modify] https://crrev.com/1e4e770ec53ab865cc8a0e85d9894f056cf8cc30/content/renderer/service_worker/service_worker_subresource_loader_unittest.cc
[modify] https://crrev.com/1e4e770ec53ab865cc8a0e85d9894f056cf8cc30/content/renderer/service_worker/worker_fetch_context_impl.cc
[modify] https://crrev.com/1e4e770ec53ab865cc8a0e85d9894f056cf8cc30/testing/buildbot/filters/mojo.fyi.network_content_browsertests.filter
[modify] https://crrev.com/1e4e770ec53ab865cc8a0e85d9894f056cf8cc30/third_party/WebKit/LayoutTests/FlagExpectations/enable-features=NetworkService

Intent to Implement and Ship: https://groups.google.com/a/chromium.org/forum/#!topic/blink-dev/zm0ZUCINXBk

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/b7591fb63d6d4cd7f30792256ac31e18c636e49c

commit b7591fb63d6d4cd7f30792256ac31e18c636e49c
Author: Marijn Kruisselbrink <mek@chromium.org>
Date: Wed Jan 31 18:46:02 2018

Failure in reading Blob URL should result in network error.

Intent to Implement and Ship: https://groups.google.com/a/chromium.org/forum/#!topic/blink-dev/zm0ZUCINXBk

Bug:  732750 
Change-Id: I07b45276f3e0ddf991f1f8a6c390bf5b843ec22e
Reviewed-on: https://chromium-review.googlesource.com/893942
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Commit-Queue: Marijn Kruisselbrink <mek@chromium.org>
Cr-Commit-Position: refs/heads/master@{#533340}
[modify] https://crrev.com/b7591fb63d6d4cd7f30792256ac31e18c636e49c/chrome/test/data/extensions/api_test/mime_handler_view/index.js
[modify] https://crrev.com/b7591fb63d6d4cd7f30792256ac31e18c636e49c/chrome/test/data/extensions/api_test/streams_private/handle_mime_type/background.js
[modify] https://crrev.com/b7591fb63d6d4cd7f30792256ac31e18c636e49c/content/browser/blob_storage/blob_url_unittest.cc
[modify] https://crrev.com/b7591fb63d6d4cd7f30792256ac31e18c636e49c/storage/browser/blob/blob_url_loader.cc
[modify] https://crrev.com/b7591fb63d6d4cd7f30792256ac31e18c636e49c/storage/browser/blob/blob_url_request_job.cc
[modify] https://crrev.com/b7591fb63d6d4cd7f30792256ac31e18c636e49c/storage/browser/blob/blob_url_request_job.h
[modify] https://crrev.com/b7591fb63d6d4cd7f30792256ac31e18c636e49c/third_party/WebKit/LayoutTests/external/wpt/FileAPI/url/url-with-xhr.any-expected.txt
[modify] https://crrev.com/b7591fb63d6d4cd7f30792256ac31e18c636e49c/third_party/WebKit/LayoutTests/fast/files/apply-blob-url-to-xhr-expected.txt
[modify] https://crrev.com/b7591fb63d6d4cd7f30792256ac31e18c636e49c/third_party/WebKit/LayoutTests/fast/files/workers/worker-apply-blob-url-to-xhr-expected.txt
[modify] https://crrev.com/b7591fb63d6d4cd7f30792256ac31e18c636e49c/third_party/WebKit/LayoutTests/http/tests/xmlhttprequest/xhr-to-blob-in-isolated-world-expected.txt
[modify] https://crrev.com/b7591fb63d6d4cd7f30792256ac31e18c636e49c/third_party/WebKit/LayoutTests/http/tests/xmlhttprequest/xhr-to-blob-in-isolated-world.html
[modify] https://crrev.com/b7591fb63d6d4cd7f30792256ac31e18c636e49c/third_party/WebKit/Source/core/fetch/FetchManager.cpp