To Ehsan for triage: does this involve oop printing?

This is not a regression, I can reproduce this in 65.0.3325.146 and even the earliest version where embedded options pages were introduced (version 40.0.2214.114).

When an extension uses options_ui, Chrome will use a <extensionoptions> custom element to render the content. It seems that the content of such elements is not rendered in the print preview.

Minimal reproduction steps:
1. Create file manifest.json with the following content:
{
    "name": "Embedded options page",
    "version": "1",
    "manifest_version": 2,
    "options_ui": {
        "page": "options.html"
    }
}

2. Create options.html with the following content:
Embedded options page.

3. Load the directory containing those two files at chrome://extensions and start the print preview

Expected: Print preview with "Embedded options page".
Actual  : The options page is not rendered.

This might be OOPIF printing given that the top overlay is an OOPIF-GuestView. Assigning to weili@ who works on OOPIF printing. Feel free to assign back to me if it is not relevant.

yes, the blank content was rendered out of process. OOPIF printing should be able to solve it. 

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/5c0b4d1a198bfc165b82ab21e2748dc7b9ea1af4

commit 5c0b4d1a198bfc165b82ab21e2748dc7b9ea1af4
Author: Wei Li <weili@chromium.org>
Date: Thu Mar 22 15:05:22 2018

Use OOPIF printing for extension/app pages

Some extension/app pages are hosted by guest views, which means they
have nested web contents. This CL checks nested web contents and always
use the outer contents to handle print requests so the entire content
can be printed correctly.

BUG= 819583 ,  447941 

Change-Id: I6b45f4867d13cf5141476a7e748e8c0e5d3b0996
Reviewed-on: https://chromium-review.googlesource.com/969949
Commit-Queue: Wei Li <weili@chromium.org>
Reviewed-by: Alex Moshchuk <alexmos@chromium.org>
Reviewed-by: Lei Zhang <thestig@chromium.org>
Cr-Commit-Position: refs/heads/master@{#545077}
[modify] https://crrev.com/5c0b4d1a198bfc165b82ab21e2748dc7b9ea1af4/chrome/browser/printing/print_browsertest.cc
[add] https://crrev.com/5c0b4d1a198bfc165b82ab21e2748dc7b9ea1af4/chrome/test/data/printing/test_extension/manifest.json
[add] https://crrev.com/5c0b4d1a198bfc165b82ab21e2748dc7b9ea1af4/chrome/test/data/printing/test_extension/options.html
[add] https://crrev.com/5c0b4d1a198bfc165b82ab21e2748dc7b9ea1af4/chrome/test/data/printing/test_extension/test_extension.html
[modify] https://crrev.com/5c0b4d1a198bfc165b82ab21e2748dc7b9ea1af4/components/printing/browser/print_composite_client.cc
[modify] https://crrev.com/5c0b4d1a198bfc165b82ab21e2748dc7b9ea1af4/content/browser/web_contents/web_contents_impl.cc
[modify] https://crrev.com/5c0b4d1a198bfc165b82ab21e2748dc7b9ea1af4/content/browser/web_contents/web_contents_impl.h
[modify] https://crrev.com/5c0b4d1a198bfc165b82ab21e2748dc7b9ea1af4/content/public/browser/web_contents.h

verified on Canary 67.0.3379.0. This change is small and affected extension/app printing only. This has been broken for a while (maybe M60?). It didn't show option page in print preview. But if site isolation is enabled, the print preview will hang until user close it. Thus request a merge into M66. thanks.

This bug requires manual review: M66 has already been promoted to the beta branch, so this requires manual review
Please contact the milestone owner if you have questions.
Owners: cmasso@(Android), cmasso@(iOS), josafat@(ChromeOS), abdulsyed@(Desktop)

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

@7
As said in comment 3, this has never worked in Chrome (all the way back to 40, where the <extensionoptions> guest view was being used).

I'm not sure whether this needs to be merged since this is a non-regression, and apparently nobody had noticed the blank pages in the print preview of chrome://extensions.

> But if site isolation is enabled, the print preview will hang until user close it.

Print preview isn't hanging here in Chrome stable with the STR from comment 3.

Re#9: The hang started after commit ef052a2f598059f95ff7151e3b62fd2a8a3b9abb, which is only in M66.

lfg@ / weili@ - is a merge still needed?

yes, pls. Otherwise, print preview will hang on extension option page for M66 trials.

Approving merge to M66. Branch:3359

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/3de8547439cdb5522a973e72dd0607c1dd7c6998

commit 3de8547439cdb5522a973e72dd0607c1dd7c6998
Author: Wei Li <weili@chromium.org>
Date: Mon Mar 26 18:40:04 2018

Use OOPIF printing for extension/app pages

Some extension/app pages are hosted by guest views, which means they
have nested web contents. This CL checks nested web contents and always
use the outer contents to handle print requests so the entire content
can be printed correctly.

BUG= 819583 ,  447941 

Change-Id: I6b45f4867d13cf5141476a7e748e8c0e5d3b0996
Reviewed-on: https://chromium-review.googlesource.com/969949
Commit-Queue: Wei Li <weili@chromium.org>
Reviewed-by: Alex Moshchuk <alexmos@chromium.org>
Reviewed-by: Lei Zhang <thestig@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#545077}(cherry picked from commit 5c0b4d1a198bfc165b82ab21e2748dc7b9ea1af4)
Reviewed-on: https://chromium-review.googlesource.com/981085
Reviewed-by: Wei Li <weili@chromium.org>
Cr-Commit-Position: refs/branch-heads/3359@{#444}
Cr-Branched-From: 66afc5e5d10127546cc4b98b9117aff588b5e66b-refs/heads/master@{#540276}
[modify] https://crrev.com/3de8547439cdb5522a973e72dd0607c1dd7c6998/chrome/browser/printing/print_browsertest.cc
[add] https://crrev.com/3de8547439cdb5522a973e72dd0607c1dd7c6998/chrome/test/data/printing/test_extension/manifest.json
[add] https://crrev.com/3de8547439cdb5522a973e72dd0607c1dd7c6998/chrome/test/data/printing/test_extension/options.html
[add] https://crrev.com/3de8547439cdb5522a973e72dd0607c1dd7c6998/chrome/test/data/printing/test_extension/test_extension.html
[modify] https://crrev.com/3de8547439cdb5522a973e72dd0607c1dd7c6998/components/printing/browser/print_composite_client.cc
[modify] https://crrev.com/3de8547439cdb5522a973e72dd0607c1dd7c6998/content/browser/web_contents/web_contents_impl.cc
[modify] https://crrev.com/3de8547439cdb5522a973e72dd0607c1dd7c6998/content/browser/web_contents/web_contents_impl.h
[modify] https://crrev.com/3de8547439cdb5522a973e72dd0607c1dd7c6998/content/public/browser/web_contents.h