Using the per-revision bisect providing the bisect results,
Good build: 56.0.2902.0 (Revision: 427892).
Bad build: 56.0.2903.0 (Revision: 428231).

You are probably looking for a change made after 428039 (known good), but no later than 428040 (first known bad).
CHANGELOG URL:
  https://chromium.googlesource.com/chromium/src/+log/2ce641d6fa80fc0a9ea2fe1484f6040224e2a6a3..e285ee2fbabbe223bb36fe96f83bdb70d93ef643

@mkwst -- Could you please look into the issue, pardon me if it has nothing to do with your changes and if possible please assign it to concern owner.

Adding RB Label as this is a recent Regression. Please remove if not required.

Thank You.

Is the experimental flag off by default? If so, this probably should not be P1 / RBS?

We have an experiment running that disables automatic whitelisting of parser-inserted 'chrome-extension://' URLs. Looks like we use the PDF extension inside an HTML Import when rendering the print preview page. +aaj@.

I agree that this is neither P1 nor a release block, but I need to get it fixed so that we get reasonable data to make a decision about the behavior change.

I've uploaded a fix at https://codereview.chromium.org/2528903002, let's see what tsepez@ thinks. :)

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/c5dd67fc5244bc8ee3fa74bea9835a0d054d2a37

commit c5dd67fc5244bc8ee3fa74bea9835a0d054d2a37
Author: mkwst <mkwst@chromium.org>
Date: Mon Nov 28 23:25:33 2016

Allow the PDF extension for chrome://print pages.

We have an experiment running that would disable parser-inserted usage
of 'chrome-extension://' URLs unless explicitly whitelisted. This breaks
the print preview page, which relies on the PDF extension URLs inside an
HTML import. So. This patch adds a mechanism for whitelisting that
extension URL for the print preview page.

BUG=667224
R=tsepez@chromium.org

Review-Url: https://codereview.chromium.org/2528903002
Cr-Commit-Position: refs/heads/master@{#434770}

[modify] https://crrev.com/c5dd67fc5244bc8ee3fa74bea9835a0d054d2a37/chrome/browser/ui/webui/print_preview/print_preview_ui.cc
[modify] https://crrev.com/c5dd67fc5244bc8ee3fa74bea9835a0d054d2a37/content/browser/webui/web_ui_data_source_impl.cc
[modify] https://crrev.com/c5dd67fc5244bc8ee3fa74bea9835a0d054d2a37/content/browser/webui/web_ui_data_source_impl.h
[modify] https://crrev.com/c5dd67fc5244bc8ee3fa74bea9835a0d054d2a37/content/public/browser/web_ui_data_source.h

 Issue 668918  has been merged into this issue.

Assuming the CL fixes the issue in tomorrow's Canary, I'll request a merge back to M56.

Tested this issue on Mac 10.12.2, Win-10 and Ubuntu 14.04 using Chrome version #57.0.2979.0 as per the comment #0.

Observed that print preview loaded instantly as expected.

Hence, the fix is working as expected.

Attaching the screencast for reference

Adding the verified labels.

mkwst@ - Could you please merge it to M56.

Thanks...!!

Deleted: 667224.mp4 1.5 MB

	667224.mp4 1.5 MB View Download

re #6: mkwst@ was this merged back to M56? I see the same issue in my M56 stable build on Linux with --enable-experimental-web-platform-features.

Looking at dev tools it is definitely "Content Security Policy directive" preventing the pdf viewer.