I did submit a patch to review for this (https://codereview.chromium.org/2852593002/).

Thanks for the CL!  I'll take care of the merge to M59 once it lands.

 Issue 707349  has been merged into this issue.

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Can you please request merge in to M59 branch if this is working correctly on ToT build ?

https://codereview.chromium.org/2852593002/ has not landed yet

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/3449c607560559da80f7ecc9c3e5b24440b9010c

commit 3449c607560559da80f7ecc9c3e5b24440b9010c
Author: thomasanderson <thomasanderson@google.com>
Date: Mon May 08 21:54:55 2017

Fix DPI scaling on Linux with GTK3

The device scale was determined by querying the value of the
"gtk-xft-dpi" property from GtkSettings. In GTK2, this always returned
the value of the "Xft/DPI" XSettings property. However, in GTK3, this
returns the value of "Gdk/UnscaledDPI" if it is set, resulting in the
wrong device scale being calculated on high DPI screens.

Instead, we now query the "gdk-window-scaling-factor" setting from
GdkScreen, which is derived from the value of the
"Gdk/WindowScalingFactor" XSettings property. If this property is not
set then we fall back to the previous code path, as environments that
don't provide Gdk/WindowScalingFactor also won't provide
Gdk/UnscaledDPI.

BUG= 716135 
TBR=erg@chromium.org

patch from issue 2852593002 at patchset 20001 (http://crrev.com/2852593002#ps20001)

Review-Url: https://codereview.chromium.org/2869763004
Cr-Commit-Position: refs/heads/master@{#470142}

[modify] https://crrev.com/3449c607560559da80f7ecc9c3e5b24440b9010c/chrome/browser/ui/libgtkui/gtk_ui.cc

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/2c2751e4ab72020be05c7089047cdc4be6cd3923

commit 2c2751e4ab72020be05c7089047cdc4be6cd3923
Author: thomasanderson <thomasanderson@chromium.org>
Date: Tue May 09 17:53:54 2017

[Merge to M59] Fix DPI scaling on Linux with GTK3

> The device scale was determined by querying the value of the
> "gtk-xft-dpi" property from GtkSettings. In GTK2, this always returned
> the value of the "Xft/DPI" XSettings property. However, in GTK3, this
> returns the value of "Gdk/UnscaledDPI" if it is set, resulting in the
> wrong device scale being calculated on high DPI screens.
>
> Instead, we now query the "gdk-window-scaling-factor" setting from
> GdkScreen, which is derived from the value of the
> "Gdk/WindowScalingFactor" XSettings property. If this property is not
> set then we fall back to the previous code path, as environments that
> don't provide Gdk/WindowScalingFactor also won't provide
> Gdk/UnscaledDPI.
>
> BUG= 716135 
> TBR=erg@chromium.org
>
> patch from issue 2852593002 at patchset 20001 (http://crrev.com/2852593002#ps20001)
>
> Review-Url: https://codereview.chromium.org/2869763004
> Cr-Commit-Position: refs/heads/master@{#470142}

BUG= 716135 
TBR=erg@chromium.org
NOTRY=true
NOPRESUBMIT=true

Review-Url: https://codereview.chromium.org/2865253004
Cr-Commit-Position: refs/branch-heads/3071@{#481}
Cr-Branched-From: a106f0abbf69dad349d4aaf4bcc4f5d376dd2377-refs/heads/master@{#464641}

[modify] https://crrev.com/2c2751e4ab72020be05c7089047cdc4be6cd3923/chrome/browser/ui/libgtkui/gtk_ui.cc

Your change meets the bar and is auto-approved for M59. Please go ahead and merge the CL to branch 3071 manually. Please contact milestone owner if you have questions.
Owners: amineer@(Android), cmasso@(iOS), gkihumba@(ChromeOS), Abdul Syed@(Desktop)

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

 Issue 717789  has been merged into this issue.

Verified this issue on Ubuntu 14.04 X1 Carbon HiDpi using chrome latest dev M60-60.0.3095.5 by following steps mentioned in the original comment. Observed the UI scaling is displayed as expected on high DPI screens with use_gtk3 build. Hence adding TE-Verified label.

	Screenshot from 2017-05-11 15_44_50.png 212 KB View Download

Please merge your change to M59 branch 3071 by 4:00 PM PT, Monday (05/15) so we can take it in for next week beta release. Thank you.

It's already merged. Not sure why it didn't remove the merge-approved tag. removing.

https://chromium.googlesource.com/chromium/src/+/2c2751e4ab72020be05c7089047cdc4be6cd3923

It's now far too large. Previously, I could have GNOME set to:

- window scaling: 2x
- font scaling: 75%

and the Chrome UI would respond accordingly.

Now it seems to be ignoring the font scaling, and so all of the UI is too large. Let me know if a new Issue is more appropriate.

In my last comment, Comment 18, I was on this build: Version 60.0.3095.5 (Official Build) dev (64-bit).

Verified the issue on Ubuntu 14.04 with build 59.0.3071.61 as mentioned in comment# 15. Scaling is displayed fine when used on high DPI screens with use_gtk3 build. 

But as per comment 18, @thomasanderson: Can you please provide an update as per comment#18.

I believe c#18 is a separate non-regression issue.  Chrome has always used the GTK font scaling value for both font and window scaling.

AFAIK there's no way to adjust the two separately.  oshima@ is this correct?

 Issue 721831  has been merged into this issue.

Yes, that is correct.

I'm not sure I understand. Chrome canary is now much larger on my system than Chrome stable. I don't see how it could not be a regression.

Anyway, I'll install Chrome stable and take a screenshot and file a new issue tonight. (And thanks for fixing this one! 2x is definitely better than 1x on the Pixel, for example.)

I concur with the above. Here's a screenshot which shows beta (on the left) now being larger than stable.

	Screenshot from 2017-05-22 15-47-10.png 714 KB View Download

I don't know why my comment (#25) was removed. It was cross-linking to the new bug that was opened for the UI being too large now: https://bugs.chromium.org/p/chromium/issues/detail?id=723931. I'm linking it here again, because this bug is still marked "Fixed".

If this comment is to be removed again, can I please understand why? Is it not allowed to crosslink bugs?