NTB configuration work is done, we just need to add it to chrome://flags.
Similarly, close buttons need to be added to chrome://flags.

Both above per conversation on configurability.

If we need to add a flag for close buttons, let's split that out of this bug.

I'd suggesting making this a normal UI option, users are very used to their new tab button position and in general dislike change so why not make it an option defaulting to the value that the design dept. deems optimal?

We're not going to be moving the NTB from the position users are used to, so if the motivation for suggesting "make it an option" is "let me put my NTB back", that's very shortly going to be moot.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/b78046188914eab12996154de10053b38e283f77

commit b78046188914eab12996154de10053b38e283f77
Author: Peter Kasting <pkasting@chromium.org>
Date: Fri Jun 29 20:15:13 2018

Show close buttons on inactive tabs by default, and add feature control for it.

Bug:  855729 ,  856667 ,  846430 
Change-Id: Id2c9da22f671c94ffce1995477cab0899217ea2b
Reviewed-on: https://chromium-review.googlesource.com/1119538
Commit-Queue: Peter Kasting <pkasting@chromium.org>
Reviewed-by: Bret Sepulveda <bsep@chromium.org>
Cr-Commit-Position: refs/heads/master@{#571607}
[modify] https://crrev.com/b78046188914eab12996154de10053b38e283f77/chrome/browser/about_flags.cc
[modify] https://crrev.com/b78046188914eab12996154de10053b38e283f77/chrome/browser/flag_descriptions.cc
[modify] https://crrev.com/b78046188914eab12996154de10053b38e283f77/chrome/browser/flag_descriptions.h
[modify] https://crrev.com/b78046188914eab12996154de10053b38e283f77/chrome/browser/ui/views/tabs/tab_close_button.cc
[modify] https://crrev.com/b78046188914eab12996154de10053b38e283f77/chrome/browser/ui/views/tabs/tab_strip.cc
[modify] https://crrev.com/b78046188914eab12996154de10053b38e283f77/chrome/common/chrome_features.cc
[modify] https://crrev.com/b78046188914eab12996154de10053b38e283f77/chrome/common/chrome_features.h
[modify] https://crrev.com/b78046188914eab12996154de10053b38e283f77/tools/metrics/histograms/enums.xml

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/630979171b981ffefd07c1e31036f322b6cb03f1

commit 630979171b981ffefd07c1e31036f322b6cb03f1
Author: Peter Kasting <pkasting@chromium.org>
Date: Sat Jun 30 02:09:03 2018

Change NTB default position to AFTER_TABS, add flags, remove Finch control.

I'm not opposed to leaving this under Finch control for future experimentation,
but I don't really know how to use FEATURE_WITH_PARAMS_VALUE.

Bug:  857610 ,  857282 ,  855729 
Change-Id: Ibe1b9c13003f2da78b241e775f37b2e9ab7e71f7
Reviewed-on: https://chromium-review.googlesource.com/1119362
Commit-Queue: Peter Kasting <pkasting@chromium.org>
Reviewed-by: Bret Sepulveda <bsep@chromium.org>
Cr-Commit-Position: refs/heads/master@{#571739}
[modify] https://crrev.com/630979171b981ffefd07c1e31036f322b6cb03f1/chrome/browser/about_flags.cc
[modify] https://crrev.com/630979171b981ffefd07c1e31036f322b6cb03f1/chrome/browser/flag_descriptions.cc
[modify] https://crrev.com/630979171b981ffefd07c1e31036f322b6cb03f1/chrome/browser/flag_descriptions.h
[modify] https://crrev.com/630979171b981ffefd07c1e31036f322b6cb03f1/chrome/browser/ui/views/tabs/browser_tab_strip_controller.cc
[modify] https://crrev.com/630979171b981ffefd07c1e31036f322b6cb03f1/chrome/browser/ui/views/tabs/tab_drag_controller_interactive_uitest.cc
[modify] https://crrev.com/630979171b981ffefd07c1e31036f322b6cb03f1/chrome/common/chrome_switches.cc
[modify] https://crrev.com/630979171b981ffefd07c1e31036f322b6cb03f1/chrome/common/chrome_switches.h
[modify] https://crrev.com/630979171b981ffefd07c1e31036f322b6cb03f1/tools/metrics/histograms/enums.xml