pri-3 is fair, but as a code health issue and performance question I still intend to address it :-)

marking as "available" as I may not get around to finishing up the relevant CLs, but anyone can pick this up:

https://codereview.chromium.org/2236463005/
https://codereview.chromium.org/2221073004/
https://codereview.chromium.org/2231593003/

I am wondering if now is a good time to address this issue. Will take a look on what would be the scale of such a change.

As noted by @michaelpg, the deprecation warning got a bit scarier lately, see attachement.

"[Deprecation] /deep/ combinator is deprecated and will be a no-op in M60, around August 2017"

I think that is one more reason to update our code.

Deleted: warning.png 26.6 KB

	warning.png 26.6 KB View Download

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/3bccef5b96b6695d40407dc3c4a2e22212730256

commit 3bccef5b96b6695d40407dc3c4a2e22212730256
Author: dpapad <dpapad@chromium.org>
Date: Wed Apr 26 00:30:11 2017

WebUI: Unify [hidden] attribute styling rules.

This CL addresses MD Settings, History, Downloads and Bookmarks.
MD Extensions will be addressed in follow up CL.

BUG= 635633 
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:closure_compilation

Review-Url: https://codereview.chromium.org/2838963003
Cr-Commit-Position: refs/heads/master@{#467180}

[modify] https://crrev.com/3bccef5b96b6695d40407dc3c4a2e22212730256/chrome/browser/resources/md_bookmarks/shared_style.html
[modify] https://crrev.com/3bccef5b96b6695d40407dc3c4a2e22212730256/chrome/browser/resources/md_downloads/item.html
[modify] https://crrev.com/3bccef5b96b6695d40407dc3c4a2e22212730256/chrome/browser/resources/md_downloads/manager.html
[modify] https://crrev.com/3bccef5b96b6695d40407dc3c4a2e22212730256/chrome/browser/resources/md_downloads/toolbar.html
[modify] https://crrev.com/3bccef5b96b6695d40407dc3c4a2e22212730256/chrome/browser/resources/md_history/shared_style.html
[modify] https://crrev.com/3bccef5b96b6695d40407dc3c4a2e22212730256/chrome/browser/resources/settings/settings_shared_css.html
[add] https://crrev.com/3bccef5b96b6695d40407dc3c4a2e22212730256/ui/webui/resources/cr_elements/hidden_style_css.html
[modify] https://crrev.com/3bccef5b96b6695d40407dc3c4a2e22212730256/ui/webui/resources/cr_elements/shared_style_css.html
[modify] https://crrev.com/3bccef5b96b6695d40407dc3c4a2e22212730256/ui/webui/resources/cr_elements_resources.grdp

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/60869ccf490d8a71bdbe64bca909b80b0348d805

commit 60869ccf490d8a71bdbe64bca909b80b0348d805
Author: dpapad <dpapad@chromium.org>
Date: Thu Apr 27 00:34:07 2017

MD Settings: Remove usage of deprecated iron-flex-layout.html.

This CL addresses all of non-CrOS UI surfaces, and powerwash_dialog which is
CrOS only. Remaining CrOS UI will be addressed in follow up CL.

BUG= 635633 
TEST=Open chrome:md-settings, look at the DevTools console, no more warnings.
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:closure_compilation

Review-Url: https://codereview.chromium.org/2840713002
Cr-Commit-Position: refs/heads/master@{#467529}

[modify] https://crrev.com/60869ccf490d8a71bdbe64bca909b80b0348d805/chrome/browser/resources/settings/appearance_page/appearance_page.html
[modify] https://crrev.com/60869ccf490d8a71bdbe64bca909b80b0348d805/chrome/browser/resources/settings/basic_page/basic_page.html
[modify] https://crrev.com/60869ccf490d8a71bdbe64bca909b80b0348d805/chrome/browser/resources/settings/controls/settings_toggle_button.html
[modify] https://crrev.com/60869ccf490d8a71bdbe64bca909b80b0348d805/chrome/browser/resources/settings/downloads_page/downloads_page.html
[modify] https://crrev.com/60869ccf490d8a71bdbe64bca909b80b0348d805/chrome/browser/resources/settings/on_startup_page/on_startup_page.html
[modify] https://crrev.com/60869ccf490d8a71bdbe64bca909b80b0348d805/chrome/browser/resources/settings/on_startup_page/startup_urls_page.html
[modify] https://crrev.com/60869ccf490d8a71bdbe64bca909b80b0348d805/chrome/browser/resources/settings/passwords_and_forms_page/passwords_and_forms_page.html
[modify] https://crrev.com/60869ccf490d8a71bdbe64bca909b80b0348d805/chrome/browser/resources/settings/people_page/people_page.html
[modify] https://crrev.com/60869ccf490d8a71bdbe64bca909b80b0348d805/chrome/browser/resources/settings/privacy_page/privacy_page.html
[modify] https://crrev.com/60869ccf490d8a71bdbe64bca909b80b0348d805/chrome/browser/resources/settings/reset_page/powerwash_dialog.html
[modify] https://crrev.com/60869ccf490d8a71bdbe64bca909b80b0348d805/chrome/browser/resources/settings/reset_page/reset_profile_dialog.html
[modify] https://crrev.com/60869ccf490d8a71bdbe64bca909b80b0348d805/chrome/browser/resources/settings/settings_main/settings_main.html
[modify] https://crrev.com/60869ccf490d8a71bdbe64bca909b80b0348d805/chrome/browser/resources/settings/settings_page/settings_animated_pages.html
[modify] https://crrev.com/60869ccf490d8a71bdbe64bca909b80b0348d805/chrome/browser/resources/settings/settings_ui/settings_ui.html
[modify] https://crrev.com/60869ccf490d8a71bdbe64bca909b80b0348d805/chrome/browser/resources/settings/site_settings/site_data.html
[modify] https://crrev.com/60869ccf490d8a71bdbe64bca909b80b0348d805/chrome/browser/resources/settings/site_settings/site_details.html

As I am converting the remaining CrOS UIs away from iron-flex-layout.html, I discovered something interesting (and unexpected).

In iron-flex-layout.html the "flex" class simply specifies "flex: 1", see [1]. On the other hand, in the new iron-flex-layout-classes.html the "flex" class also specifies an odd flex-basis value of 0.000000001px, which breaks some of our UIs. 

[1] https://github.com/PolymerElements/iron-flex-layout/blob/master/classes/iron-flex-layout.html#L92
[2] https://github.com/PolymerElements/iron-flex-layout/blob/master/iron-flex-layout-classes.html#L89

Posted a question at https://github.com/PolymerElements/iron-flex-layout/issues/87#issuecomment-297827988 about it.

 Issue 715407  has been merged into this issue.

Increasing priority to match that of  issue 715407 .

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/abeb3b928b8834dd180f8b75ccca53b52d6cde55

commit abeb3b928b8834dd180f8b75ccca53b52d6cde55
Author: dpapad <dpapad@chromium.org>
Date: Mon May 01 23:24:56 2017

MD Settings: Remove usage of deprecated iron-flex-layout.html, for CrOS.

BUG= 635633 
TEST=Open chrome:md-settings, look at the DevTools console, no more warnings.
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:closure_compilation

Review-Url: https://codereview.chromium.org/2848443002
Cr-Commit-Position: refs/heads/master@{#468480}

[modify] https://crrev.com/abeb3b928b8834dd180f8b75ccca53b52d6cde55/chrome/browser/resources/settings/bluetooth_page/bluetooth_device_dialog.html
[modify] https://crrev.com/abeb3b928b8834dd180f8b75ccca53b52d6cde55/chrome/browser/resources/settings/bluetooth_page/bluetooth_device_list_item.html
[modify] https://crrev.com/abeb3b928b8834dd180f8b75ccca53b52d6cde55/chrome/browser/resources/settings/bluetooth_page/bluetooth_page.html
[modify] https://crrev.com/abeb3b928b8834dd180f8b75ccca53b52d6cde55/chrome/browser/resources/settings/bluetooth_page/bluetooth_subpage.html
[modify] https://crrev.com/abeb3b928b8834dd180f8b75ccca53b52d6cde55/chrome/browser/resources/settings/device_page/display.html
[modify] https://crrev.com/abeb3b928b8834dd180f8b75ccca53b52d6cde55/chrome/browser/resources/settings/device_page/display_overscan_dialog.html
[modify] https://crrev.com/abeb3b928b8834dd180f8b75ccca53b52d6cde55/chrome/browser/resources/settings/internet_page/internet_detail_page.html
[modify] https://crrev.com/abeb3b928b8834dd180f8b75ccca53b52d6cde55/chrome/browser/resources/settings/internet_page/internet_known_networks_page.html
[modify] https://crrev.com/abeb3b928b8834dd180f8b75ccca53b52d6cde55/chrome/browser/resources/settings/internet_page/internet_page.html
[modify] https://crrev.com/abeb3b928b8834dd180f8b75ccca53b52d6cde55/chrome/browser/resources/settings/internet_page/internet_subpage.html
[modify] https://crrev.com/abeb3b928b8834dd180f8b75ccca53b52d6cde55/chrome/browser/resources/settings/internet_page/network_proxy.html
[modify] https://crrev.com/abeb3b928b8834dd180f8b75ccca53b52d6cde55/chrome/browser/resources/settings/internet_page/network_proxy_exclusions.html
[modify] https://crrev.com/abeb3b928b8834dd180f8b75ccca53b52d6cde55/chrome/browser/resources/settings/people_page/user_list.html
[modify] https://crrev.com/abeb3b928b8834dd180f8b75ccca53b52d6cde55/chrome/browser/resources/settings/people_page/users_page.html
[modify] https://crrev.com/abeb3b928b8834dd180f8b75ccca53b52d6cde55/ui/webui/resources/cr_elements/network/cr_network_icon.html
[modify] https://crrev.com/abeb3b928b8834dd180f8b75ccca53b52d6cde55/ui/webui/resources/cr_elements/network/cr_network_list.html
[modify] https://crrev.com/abeb3b928b8834dd180f8b75ccca53b52d6cde55/ui/webui/resources/cr_elements/network/cr_network_list_item.html
[modify] https://crrev.com/abeb3b928b8834dd180f8b75ccca53b52d6cde55/ui/webui/resources/cr_elements/network/cr_network_select.html
[modify] https://crrev.com/abeb3b928b8834dd180f8b75ccca53b52d6cde55/ui/webui/resources/cr_elements/network/cr_network_select.js
[modify] https://crrev.com/abeb3b928b8834dd180f8b75ccca53b52d6cde55/ui/webui/resources/cr_elements/policy/cr_policy_indicator.html
[modify] https://crrev.com/abeb3b928b8834dd180f8b75ccca53b52d6cde55/ui/webui/resources/cr_elements/policy/cr_policy_network_indicator.html
[modify] https://crrev.com/abeb3b928b8834dd180f8b75ccca53b52d6cde55/ui/webui/resources/cr_elements/policy/cr_policy_pref_indicator.html

@hayato: I believe that all the test failures you were seeing should be fixed now. Let me know if you are still having issues.

dpapad@, thank you for fixing this!