Doug, is there any progress being made on this?

Yes, Nate and Egor lgtm-ed CL about an hour ago.
I pinged Dmitry for any comments on the CL. Interested if you have any comments as well (youare listed as reviewer).

lgtm, please land and merge :)

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/f1ba435af9338792a78fc422eb9cd1a51a14aa13

commit f1ba435af9338792a78fc422eb9cd1a51a14aa13
Author: dougarnett <dougarnett@chromium.org>
Date: Thu Feb 09 17:28:37 2017

[Prerender] Ignores resources with unsupported schemes for Offline reqs

For offlining a page with the prerender, this changes the policy when
encountering a resource with an unsupported scheme - instread of failing
the prerender (as is done with other prerender requests), it will only
cancel the unsupported resource and attempt to continue with prerendering.

This has been tested end-end on 5 articles linked from www.foxsports.com
that have a "blob:" subresource and with this change, we are able to
download and offline version of them.

BUG= 686192 

Review-Url: https://codereview.chromium.org/2661703002
Cr-Commit-Position: refs/heads/master@{#449337}

[modify] https://crrev.com/f1ba435af9338792a78fc422eb9cd1a51a14aa13/chrome/browser/prerender/prerender_browsertest.cc
[modify] https://crrev.com/f1ba435af9338792a78fc422eb9cd1a51a14aa13/chrome/browser/prerender/prerender_resource_throttle.cc

Your change meets the bar and is auto-approved for M57. Please go ahead and merge the CL to branch 2987 manually. Please contact milestone owner if you have questions.
Owners: amineer@(clank), cmasso@(bling), ketakid@(cros), govind@(desktop)

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/0aeb5cf9de7fd0003d7a4323ab46e5e10d500d30

commit 0aeb5cf9de7fd0003d7a4323ab46e5e10d500d30
Author: Pete Williamson <petewil@chromium.org>
Date: Thu Feb 09 21:27:00 2017

[Prerender] Ignores resources with unsupported schemes for Offline reqs

For offlining a page with the prerender, this changes the policy when
encountering a resource with an unsupported scheme - instread of failing
the prerender (as is done with other prerender requests), it will only
cancel the unsupported resource and attempt to continue with prerendering.

This has been tested end-end on 5 articles linked from www.foxsports.com
that have a "blob:" subresource and with this change, we are able to
download and offline version of them.

BUG= 686192 

Review-Url: https://codereview.chromium.org/2661703002
Cr-Commit-Position: refs/heads/master@{#449337}
(cherry picked from commit f1ba435af9338792a78fc422eb9cd1a51a14aa13)

Review-Url: https://codereview.chromium.org/2687173002 .
Cr-Commit-Position: refs/branch-heads/2987@{#417}
Cr-Branched-From: ad51088c0e8776e8dcd963dbe752c4035ba6dab6-refs/heads/master@{#444943}

[modify] https://crrev.com/0aeb5cf9de7fd0003d7a4323ab46e5e10d500d30/chrome/browser/prerender/prerender_browsertest.cc
[modify] https://crrev.com/0aeb5cf9de7fd0003d7a4323ab46e5e10d500d30/chrome/browser/prerender/prerender_resource_throttle.cc