I don't know exactly what's involved but this should be fairly low-effort, I believe it's just creating a "configuration" that tells Finch about the flag but you'll have to ask Finch team about this.

Lets get this in before branch this Thursday.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/f8b7dc953a79f8565fde8cd22642b000a236d5a5

commit f8b7dc953a79f8565fde8cd22642b000a236d5a5
Author: chaopeng <chaopeng@chromium.org>
Date: Thu Apr 20 02:23:43 2017

Convert the overlay scrollbar flag to use FeatureList

Current implementation uses an old-styled field trial flag.
To make server side configurations and client side flag handling easy
and clear, convert the field trial flag to use FeatureList.

BUG= 710060 

Review-Url: https://codereview.chromium.org/2806263005
Cr-Commit-Position: refs/heads/master@{#465867}

[modify] https://crrev.com/f8b7dc953a79f8565fde8cd22642b000a236d5a5/chrome/browser/about_flags.cc
[modify] https://crrev.com/f8b7dc953a79f8565fde8cd22642b000a236d5a5/chrome/renderer/autofill/form_classifier_browsertest.cc
[modify] https://crrev.com/f8b7dc953a79f8565fde8cd22642b000a236d5a5/chrome/renderer/safe_browsing/phishing_dom_feature_extractor_browsertest.cc
[modify] https://crrev.com/f8b7dc953a79f8565fde8cd22642b000a236d5a5/chrome/renderer/safe_browsing/threat_dom_details_browsertest.cc
[modify] https://crrev.com/f8b7dc953a79f8565fde8cd22642b000a236d5a5/content/browser/android/content_startup_flags.cc
[modify] https://crrev.com/f8b7dc953a79f8565fde8cd22642b000a236d5a5/content/browser/renderer_host/render_process_host_impl.cc
[modify] https://crrev.com/f8b7dc953a79f8565fde8cd22642b000a236d5a5/content/browser/renderer_host/render_view_host_impl.cc
[modify] https://crrev.com/f8b7dc953a79f8565fde8cd22642b000a236d5a5/content/browser/site_per_process_browsertest.cc
[modify] https://crrev.com/f8b7dc953a79f8565fde8cd22642b000a236d5a5/content/browser/site_per_process_browsertest.h
[modify] https://crrev.com/f8b7dc953a79f8565fde8cd22642b000a236d5a5/content/child/runtime_features.cc
[modify] https://crrev.com/f8b7dc953a79f8565fde8cd22642b000a236d5a5/content/renderer/gpu/render_widget_compositor.cc
[modify] https://crrev.com/f8b7dc953a79f8565fde8cd22642b000a236d5a5/content/renderer/render_view_browsertest.cc
[modify] https://crrev.com/f8b7dc953a79f8565fde8cd22642b000a236d5a5/third_party/WebKit/LayoutTests/VirtualTestSuites
[modify] https://crrev.com/f8b7dc953a79f8565fde8cd22642b000a236d5a5/tools/metrics/histograms/histograms.xml
[modify] https://crrev.com/f8b7dc953a79f8565fde8cd22642b000a236d5a5/ui/native_theme/BUILD.gn
[modify] https://crrev.com/f8b7dc953a79f8565fde8cd22642b000a236d5a5/ui/native_theme/native_theme_aura.cc
[add] https://crrev.com/f8b7dc953a79f8565fde8cd22642b000a236d5a5/ui/native_theme/native_theme_features.cc
[add] https://crrev.com/f8b7dc953a79f8565fde8cd22642b000a236d5a5/ui/native_theme/native_theme_features.h
[delete] https://crrev.com/263834d72b249d94e0c60896d1568c3b30344821/ui/native_theme/native_theme_switches.cc
[delete] https://crrev.com/263834d72b249d94e0c60896d1568c3b30344821/ui/native_theme/native_theme_switches.h

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/d3ca34febe2838703bfd71217be83fb26e372257

commit d3ca34febe2838703bfd71217be83fb26e372257
Author: chaopeng <chaopeng@chromium.org>
Date: Thu Apr 20 17:11:22 2017

Convert the overlay scrollbar flag to use FeatureList

Current implementation uses an old-styled field trial flag.
To make server side configurations and client side flag handling easy
and clear, convert the field trial flag to use FeatureList.

BUG= 710060 

Review-Url: https://codereview.chromium.org/2806263005
Cr-Original-Commit-Position: refs/heads/master@{#465867}
Committed: https://chromium.googlesource.com/chromium/src/+/f8b7dc953a79f8565fde8cd22642b000a236d5a5
Review-Url: https://codereview.chromium.org/2806263005
Cr-Commit-Position: refs/heads/master@{#466032}

[modify] https://crrev.com/d3ca34febe2838703bfd71217be83fb26e372257/chrome/browser/about_flags.cc
[modify] https://crrev.com/d3ca34febe2838703bfd71217be83fb26e372257/chrome/renderer/autofill/form_classifier_browsertest.cc
[modify] https://crrev.com/d3ca34febe2838703bfd71217be83fb26e372257/chrome/renderer/safe_browsing/phishing_dom_feature_extractor_browsertest.cc
[modify] https://crrev.com/d3ca34febe2838703bfd71217be83fb26e372257/chrome/renderer/safe_browsing/threat_dom_details_browsertest.cc
[modify] https://crrev.com/d3ca34febe2838703bfd71217be83fb26e372257/content/browser/android/content_startup_flags.cc
[modify] https://crrev.com/d3ca34febe2838703bfd71217be83fb26e372257/content/browser/renderer_host/render_process_host_impl.cc
[modify] https://crrev.com/d3ca34febe2838703bfd71217be83fb26e372257/content/browser/renderer_host/render_view_host_impl.cc
[modify] https://crrev.com/d3ca34febe2838703bfd71217be83fb26e372257/content/browser/site_per_process_browsertest.cc
[modify] https://crrev.com/d3ca34febe2838703bfd71217be83fb26e372257/content/browser/site_per_process_browsertest.h
[modify] https://crrev.com/d3ca34febe2838703bfd71217be83fb26e372257/content/child/runtime_features.cc
[modify] https://crrev.com/d3ca34febe2838703bfd71217be83fb26e372257/content/renderer/gpu/render_widget_compositor.cc
[modify] https://crrev.com/d3ca34febe2838703bfd71217be83fb26e372257/content/renderer/render_view_browsertest.cc
[modify] https://crrev.com/d3ca34febe2838703bfd71217be83fb26e372257/third_party/WebKit/LayoutTests/VirtualTestSuites
[modify] https://crrev.com/d3ca34febe2838703bfd71217be83fb26e372257/tools/metrics/histograms/histograms.xml
[modify] https://crrev.com/d3ca34febe2838703bfd71217be83fb26e372257/ui/native_theme/BUILD.gn
[modify] https://crrev.com/d3ca34febe2838703bfd71217be83fb26e372257/ui/native_theme/native_theme_aura.cc
[add] https://crrev.com/d3ca34febe2838703bfd71217be83fb26e372257/ui/native_theme/native_theme_features.cc
[add] https://crrev.com/d3ca34febe2838703bfd71217be83fb26e372257/ui/native_theme/native_theme_features.h
[delete] https://crrev.com/723dbf022b3038d9241fbf7767b46b61c0085e39/ui/native_theme/native_theme_switches.cc
[delete] https://crrev.com/723dbf022b3038d9241fbf7767b46b61c0085e39/ui/native_theme/native_theme_switches.h

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

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/4f893a90dfd9a7516668644fe386e8a3d55aaeea

commit 4f893a90dfd9a7516668644fe386e8a3d55aaeea
Author: David Bokan <bokan@chromium.org>
Date: Fri Apr 21 17:36:27 2017

Convert the overlay scrollbar flag to use FeatureList

Current implementation uses an old-styled field trial flag.
To make server side configurations and client side flag handling easy
and clear, convert the field trial flag to use FeatureList.

BUG= 710060 

Review-Url: https://codereview.chromium.org/2806263005
Cr-Original-Commit-Position: refs/heads/master@{#465867}
Committed: https://chromium.googlesource.com/chromium/src/+/f8b7dc953a79f8565fde8cd22642b000a236d5a5
Review-Url: https://codereview.chromium.org/2806263005
Cr-Commit-Position: refs/heads/master@{#466032}
(cherry picked from commit d3ca34febe2838703bfd71217be83fb26e372257)

Review-Url: https://codereview.chromium.org/2835683002 .
Cr-Commit-Position: refs/branch-heads/3071@{#122}
Cr-Branched-From: a106f0abbf69dad349d4aaf4bcc4f5d376dd2377-refs/heads/master@{#464641}

[modify] https://crrev.com/4f893a90dfd9a7516668644fe386e8a3d55aaeea/chrome/browser/about_flags.cc
[modify] https://crrev.com/4f893a90dfd9a7516668644fe386e8a3d55aaeea/chrome/renderer/autofill/form_classifier_browsertest.cc
[modify] https://crrev.com/4f893a90dfd9a7516668644fe386e8a3d55aaeea/chrome/renderer/safe_browsing/phishing_dom_feature_extractor_browsertest.cc
[modify] https://crrev.com/4f893a90dfd9a7516668644fe386e8a3d55aaeea/chrome/renderer/safe_browsing/threat_dom_details_browsertest.cc
[modify] https://crrev.com/4f893a90dfd9a7516668644fe386e8a3d55aaeea/content/browser/android/content_startup_flags.cc
[modify] https://crrev.com/4f893a90dfd9a7516668644fe386e8a3d55aaeea/content/browser/renderer_host/render_process_host_impl.cc
[modify] https://crrev.com/4f893a90dfd9a7516668644fe386e8a3d55aaeea/content/browser/renderer_host/render_view_host_impl.cc
[modify] https://crrev.com/4f893a90dfd9a7516668644fe386e8a3d55aaeea/content/browser/site_per_process_browsertest.cc
[modify] https://crrev.com/4f893a90dfd9a7516668644fe386e8a3d55aaeea/content/browser/site_per_process_browsertest.h
[modify] https://crrev.com/4f893a90dfd9a7516668644fe386e8a3d55aaeea/content/child/runtime_features.cc
[modify] https://crrev.com/4f893a90dfd9a7516668644fe386e8a3d55aaeea/content/renderer/gpu/render_widget_compositor.cc
[modify] https://crrev.com/4f893a90dfd9a7516668644fe386e8a3d55aaeea/content/renderer/render_view_browsertest.cc
[modify] https://crrev.com/4f893a90dfd9a7516668644fe386e8a3d55aaeea/third_party/WebKit/LayoutTests/VirtualTestSuites
[modify] https://crrev.com/4f893a90dfd9a7516668644fe386e8a3d55aaeea/tools/metrics/histograms/histograms.xml
[modify] https://crrev.com/4f893a90dfd9a7516668644fe386e8a3d55aaeea/ui/native_theme/BUILD.gn
[modify] https://crrev.com/4f893a90dfd9a7516668644fe386e8a3d55aaeea/ui/native_theme/native_theme_aura.cc
[add] https://crrev.com/4f893a90dfd9a7516668644fe386e8a3d55aaeea/ui/native_theme/native_theme_features.cc
[add] https://crrev.com/4f893a90dfd9a7516668644fe386e8a3d55aaeea/ui/native_theme/native_theme_features.h
[delete] https://crrev.com/5f662891d23246fb57e349185b57cfa663a9db6b/ui/native_theme/native_theme_switches.cc
[delete] https://crrev.com/5f662891d23246fb57e349185b57cfa663a9db6b/ui/native_theme/native_theme_switches.h

Ok, merge looks like it went in. Git Drover did spit out some errors when I did it but it looks like the patch did get cherry-picked into the branch. I'll file a separate bug for that but here's the error output:

Attempt 1 of 3
Fetching origin/refs/branch-heads/3071...
Cherry-picking commit on top of latest refs/branch-heads/3071
To https://chromium.googlesource.com/chromium/src.git
!	HEAD:refs/branch-heads/3071	[remote rejected] (error in Gerrit backend)
Done

Attempt 2 of 3
Fetching origin/refs/branch-heads/3071...
Cherry-picking commit on top of latest refs/branch-heads/3071
To https://chromium.googlesource.com/chromium/src.git
!	HEAD:refs/branch-heads/3071	[rejected] (non-fast-forward)
Done

Attempt 3 of 3
Fetching origin/refs/branch-heads/3071...
Cherry-picking commit on top of latest refs/branch-heads/3071
Your patch doesn't apply cleanly to 'refs/branch-heads/3071' HEAD @ 4f893a90dfd9a7516668644fe386e8a3d55aaeea, the following files have merge conflicts:

Please rebase your patch and try again.
Failed to push. If this persists, please file a bug.
Error: Command 'cl land --bypass-hooks' failed: Command '['git', 'cl', 'land', '--bypass-hooks']' returned non-zero exit status 1

bokan@ Trying to verify this bug. Could you provide verification steps?

You can start Chrome from command line with flags "--enable-features=OverlayScrollbar --enable-prefer-compositing-to-lcd-text" then you will see overlay scrollbar.

Thanks chaopeng@ 

Could you let me know the command to start Chrome from command line? 

This is an internal change and not user visible so there's no need for verification. 

Thanks bokan@ chaopeng@ 

Closing the bug.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/3b3488538d7cb7ba21ee3766b7a4454df7f5c39a

commit 3b3488538d7cb7ba21ee3766b7a4454df7f5c39a
Author: David Bokan <bokan@chromium.org>
Date: Mon Jun 26 21:12:31 2017

Update overlay scrollbar flag name.

The flag changed to a feature flag. Was --enable-overlay-scrollbar. Is
now --enable-feature=OverlayScrollbar.

Bug:  710060 
Change-Id: I4bd9d4284de0d506b9195d8e2311b7e1906b89e1
Reviewed-on: https://chromium-review.googlesource.com/549021
Commit-Queue: Dave Tapuska <dtapuska@chromium.org>
Reviewed-by: Dave Tapuska <dtapuska@chromium.org>
Cr-Commit-Position: refs/heads/master@{#482400}
[modify] https://crrev.com/3b3488538d7cb7ba21ee3766b7a4454df7f5c39a/third_party/WebKit/LayoutTests/fast/block/float/float-change-composited-scrolling-expected.html
[modify] https://crrev.com/3b3488538d7cb7ba21ee3766b7a4454df7f5c39a/third_party/WebKit/LayoutTests/fast/block/float/float-change-composited-scrolling.html