michaelcubel@ if possible can you please provide the machine GPU details which can be found under "chrome://gpu" and save the page as html and attach to the bug.

Unable to reproduce the issue on Win-10 using chrome reported version #65.0.3325.146 and latest canary #67.0.3364.0.

Attached a screen shot and gpu_details for reference.

Following are the steps followed to reproduce the issue.
------------
1. Opened Chrome
2. Had 2+ tabs open
3. Observed that inactive tabs doesn't have blurred titles.

michaelcubel@ - Could you please check the issue on latest canary #67.0.3364.0 by creating a new profile without any apps and extensions and please let us know if the issue still persist or not.

Thanks...!!

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Something has caused the background tab color to have a non-opaque alpha value.

This is probably a bad Chrome theme.  Reporter, can you say what Chrome theme you are using?  We'll want to test this, and if necessary, clamp the alpha value locally to prevent this from happening.

That would make perfect sense. I just got a new laptop today and after signing into chrome, the theme was applied and I just now noticed the tabs. Here is the theme: https://chrome.google.com/webstore/detail/space-lagoon/balmhbonohcljflhinodkindpfmcdlie?utm_source=gmail

Thank you for providing more feedback. Adding the requester to the cc list.

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

I can repro on my Win 10 box with that theme.  I don't think we want to allow alpha in at least this particular theme color.

(We probably don't want alpha in any theme colors.  Also I feel like this general topic has come up before and maybe there are other bugs on it.)

I'm kicking this to estade as chief theme person to decide how widespread of a fix to do.

 Issue 820253  has been merged into this issue.

Able to reproduce the issue on latest Chrome Stable i.e., 65.0.3325.146 on Windows10 machine with theme provided in comment#8.  The same works find on previous stable i.e., 64.0.3282.186.

Working on bisect now will update the bisect result soon.

I am not currently tagging the bug with blocker label based on comment#10.

Applying "RBS" label per comment #14.

I don't understand how comment 15 makes sense in light of comment 14.

I think we could just turn of anti-aliasing on that text. It's not clear that a color is wrong, as the background tab is a tint rather than a color. I think the background tab image might be transparent. However, that's probably an intentional choice by the theme author because they want the frame color/image to show through. As such, they'd probably rather us disable subpixel AA. I suggest doing so only if we're using a custom theme and there's a custom PRS_THEME_TAB_BACKGROUND/PRS_THEME_TAB_BACKGROUND_INCOGNITO.

Sorry my bad, I misread comment #14. 

Based on comment 13, this is a regression from the previous stable, and based on how I've gotten more than one bug on it today, I think it should be RBS.

I'd like to see the results of the bisect.  That should tell us what the cause is here.

Interesting,I see that issue is present in very first M65 build.

I don't think this comment is correct: https://cs.chromium.org/chromium/src/chrome/browser/ui/views/tabs/tab_strip.cc?rcl=e2502ab0e1d1af2a4f70b485f5088b03efdfe748&l=1082

that was added here: https://codereview.chromium.org/1506203008

That's how I knew so quickly that this was due to a non-opaque background -- I remember that comment.  It's supposed to always hold.  It think until recently it did.

Bisect result :
You are probably looking for a change made after 521074 (known good), but no later than 521075 (first known bad).
CHANGELOG URL:
The script might not always return single CL as suspect as some perf builds might get missing due to failure.
  https://chromium.googlesource.com/chromium/src/+log/7ea5bb7e156d45d9ac2ba7584f5a3b67af3685e5..8e794a51958551213301f32e87ff264acf644ab7

The bisect points at https://chromium-review.googlesource.com/c/chromium/src/+/802522 .  My suspicion is that this exposed a pre-existing problem to a wider set of machines.  I bet the theme provides a transparent IDR_THEME_TAB_BACKGROUND but not a transparent IDR_THEME_TAB_BACKGROUND_V, and the change to TabStripImpl::GetBackgroundResourceId() causes us to start using the former instead of the latter on Win 8+.

If I'm correct, that would mean this already might have been broken on pre-Win8 with non-glass frames (e.g. Win 7 Aero Basic).

Able to reproduce the issue after adding theme: https://chrome.google.com/webstore/detail/space-lagoon/balmhbonohcljflhinodkindpfmcdlie?utm_source=gmail on Win-10 using chrome reported version #65.0.3325.146. Able to reproduce the issue in latest beta #65.0.3325.125, latest dev #66.0.3355.0 and latest canary #67.0.3365.0.
Issue is not seen in OS-Mac and OS-Linux. 
Removing the Needs-Bisect label as bisect results has been provided at comment #23.

Thanks...!!

This bug is currently marked as M65 stable blocker and we're planning M65 Stable release next week. Pls try to land the fix ASAP to trunk and ready for merge by EOD Monday, 03/13/18. Thank you.

Verified that the theme has a custom IDR_THEME_TAB_BACKGROUND but not IDR_THEME_TAB_BACKGROUND_V or IDR_THEME_FRAME.

I could probably have something merged, but I don't think my local fix is safe enough to go into a stable release next week; it could have larger effects on themes.  Kicking this to M66.

Friendly ping to get an update on this issue as it is marked as stable blocker.

Thanks..!

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/d0fdb25b296f5aa7440891800c6fcc919331a169

commit d0fdb25b296f5aa7440891800c6fcc919331a169
Author: Peter Kasting <pkasting@chromium.org>
Date: Tue Mar 20 16:41:03 2018

Composite theme tab background images against default frame color.

This ensures the background images drawn by Tab will not be transparent even if
they are transparent in the original theme.  Tab assumes its background is fully
opaque, so that subpixel AA is guaranteed to work.

BUG= 819865 
TEST=Install theme in bug comment 25, verify background tab text is readable

Change-Id: If75228398b9ae05b275e530c3900b087a5f94139
Reviewed-on: https://chromium-review.googlesource.com/969835
Reviewed-by: Evan Stade <estade@chromium.org>
Commit-Queue: Peter Kasting <pkasting@chromium.org>
Cr-Commit-Position: refs/heads/master@{#544403}
[modify] https://crrev.com/d0fdb25b296f5aa7440891800c6fcc919331a169/chrome/browser/themes/browser_theme_pack.cc

I'd like to wait a bit to make sure we don't get unexpected theme breakage, then the fix in comment 29 can be merged to M66.

Able to reproduce the issue on Win-10 using chrome reported version #65.0.3325.146.

Verified the fix on Win-10 using Chrome version #67.0.3377.0 as per the comment #25.
Attaching screen cast for reference.
Observed that tab titles remain unblurred on adding theme: https://chrome.google.com/webstore/detail/space-lagoon/balmhbonohcljflhinodkindpfmcdlie?utm_source=gmail
Hence, the fix is working as expected. 
Adding the verified labels.

Thanks...!!

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As it is WAI on M67, requesting merge to 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

Approving merge to M66. Branch:3359

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/15b677da25cac1797a8e88ea89046b76bc3b06f0

commit 15b677da25cac1797a8e88ea89046b76bc3b06f0
Author: Peter Kasting <pkasting@chromium.org>
Date: Mon Mar 26 21:06:59 2018

Composite theme tab background images against default frame color.

This ensures the background images drawn by Tab will not be transparent even if
they are transparent in the original theme.  Tab assumes its background is fully
opaque, so that subpixel AA is guaranteed to work.

BUG= 819865 
TEST=Install theme in bug comment 25, verify background tab text is readable

Change-Id: If75228398b9ae05b275e530c3900b087a5f94139
Reviewed-on: https://chromium-review.googlesource.com/969835
Reviewed-by: Evan Stade <estade@chromium.org>
Commit-Queue: Peter Kasting <pkasting@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#544403}(cherry picked from commit d0fdb25b296f5aa7440891800c6fcc919331a169)
Reviewed-on: https://chromium-review.googlesource.com/980897
Reviewed-by: Peter Kasting <pkasting@chromium.org>
Cr-Commit-Position: refs/branch-heads/3359@{#452}
Cr-Branched-From: 66afc5e5d10127546cc4b98b9117aff588b5e66b-refs/heads/master@{#540276}
[modify] https://crrev.com/15b677da25cac1797a8e88ea89046b76bc3b06f0/chrome/browser/themes/browser_theme_pack.cc

Tested this issue on Windows 10 on the reported version 65.0.3325.146 and latest Beta 66.0.3359.66.
Able to reproduce this issue on the reported version 65.0.3325.146 and the issue is fixed on the latest Beta 66.0.3359.66.

On adding the theme https://chrome.google.com/webstore/detail/space-lagoon/balmhbonohcljflhinodkindpfmcdlie?utm_source=gmail, can observe that the tab titles remain unblurred.
Attached is the screen shot for reference.

Hence adding TE verified labels as the fix is working as intended.

Thanks..

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