The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/9b423c7bae3bee3ec8ea75fc623caa11279f7f20

commit 9b423c7bae3bee3ec8ea75fc623caa11279f7f20
Author: Fabio Tirelo <ftirelo@chromium.org>
Date: Wed Aug 15 14:32:18 2018

[Autofill Styles] Add feature and flag to allow style selection

This CL:
 - Creates a new feature/flag to allow customization of the text
   and background colors when a field shows an Autofill suggestion;
   Each color is defined by its own parameter in the study.
 - Moves the previous style from html.css and build the CSS rules
   instead in LayoutTheme::ExtraDefaultStyleSheet using either the
   colors defined by the parameters (when the feature is enabled)
   or the current preview colors as a fallback (default and
   invalid color cases).

Variations provided for the new chrome://flags entry correspond to
the experiment palletes proposed by UX (see details on the bug).

One alternative that I considered:
 - Define a single param in the study for the experiment group
   (so flag variations and param values would have a 1:1
   correspondence);
 - Define a separate CSS file for each variation, similar to what's
   currently done LayoutThemeDefault::ExtraDefaultStyleSheet.

That alternative would be less flexible, but it would be more
similar cases handled in blink (in fact, I couldn't find any place
where the CSS is built in the code). Please let me know if you think
that alternative should be used instead.

Bug: 874094
Change-Id: I257c72b9a3db32a2945ec4048e46b23e4b5dd2be
Reviewed-on: https://chromium-review.googlesource.com/1174710
Commit-Queue: Fabio Tirelo <ftirelo@chromium.org>
Reviewed-by: Kent Tamura <tkent@chromium.org>
Cr-Commit-Position: refs/heads/master@{#583243}
[modify] https://crrev.com/9b423c7bae3bee3ec8ea75fc623caa11279f7f20/chrome/browser/about_flags.cc
[modify] https://crrev.com/9b423c7bae3bee3ec8ea75fc623caa11279f7f20/chrome/browser/flag_descriptions.cc
[modify] https://crrev.com/9b423c7bae3bee3ec8ea75fc623caa11279f7f20/chrome/browser/flag_descriptions.h
[modify] https://crrev.com/9b423c7bae3bee3ec8ea75fc623caa11279f7f20/third_party/blink/common/features.cc
[modify] https://crrev.com/9b423c7bae3bee3ec8ea75fc623caa11279f7f20/third_party/blink/public/common/features.h
[modify] https://crrev.com/9b423c7bae3bee3ec8ea75fc623caa11279f7f20/third_party/blink/renderer/core/css/html.css
[modify] https://crrev.com/9b423c7bae3bee3ec8ea75fc623caa11279f7f20/third_party/blink/renderer/core/layout/layout_theme.cc
[modify] https://crrev.com/9b423c7bae3bee3ec8ea75fc623caa11279f7f20/tools/metrics/histograms/enums.xml

This is done.

To test it:
 - Have at least on address in chrome://settings/autofill
 - Enable one of the options in chrome://flags#autofill-preview-style (for example, you can choose "Enabled (GoogleBlue900 on GoogleBlue050)" and restart the browser
 - Navigate to https://dump-truck.appspot.com/usecase-address_and_cc_on_same_page/address_and_cc.html
 - At the top of the page, click on field "Name"
 - When the Autofill dropdown is shown hover on a suggestion

The suggestion preview on the input field will show up as dark blue on a light blue background, as opposed to black on a yellow blackground as we do today.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/685952aa5199fdec0a75b2e0bc8f1b35340beb49

commit 685952aa5199fdec0a75b2e0bc8f1b35340beb49
Author: Fabio Tirelo <ftirelo@chromium.org>
Date: Thu Aug 16 22:14:54 2018

[Autofill Styles] Fix typo in flag selection color

Bug: 874094
Change-Id: I246b33a817bb87357acb9b9426add41323cb2711
Reviewed-on: https://chromium-review.googlesource.com/1178748
Reviewed-by: Tommy Martino <tmartino@chromium.org>
Commit-Queue: Fabio Tirelo <ftirelo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#583848}
[modify] https://crrev.com/685952aa5199fdec0a75b2e0bc8f1b35340beb49/chrome/browser/about_flags.cc

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/0ae16d2d5e2b1c23d872a44a0b79be598591ca46

commit 0ae16d2d5e2b1c23d872a44a0b79be598591ca46
Author: Fabio Tirelo <ftirelo@chromium.org>
Date: Fri Sep 28 19:31:49 2018

Add field trial config for AutofillPreviewStyleExperiment

Bug: 874094
Change-Id: Id80332c84f574b70ba0b0e50f54aebb681276082
Reviewed-on: https://chromium-review.googlesource.com/1251229
Reviewed-by: Jesse Doherty <jwd@chromium.org>
Commit-Queue: Fabio Tirelo <ftirelo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#595179}
[modify] https://crrev.com/0ae16d2d5e2b1c23d872a44a0b79be598591ca46/testing/variations/fieldtrial_testing_config.json

We need more information in order for test team to test this feature, 
also we don't have access to chrome://settings/autofill.

shbarezer@: What information do you need? Which platform are you testing on? On Desktop, you can access chrome://settings/autofill by typing the URL on the omnibox.

On mobile, you can access from Settings > Addresses and more.

I am verifying the fix on iOS on 71.0.3568.0 Canary, and the missing information  is the chrome://flags mentioned in comment #2: #autofill-preview-style - I don't see that on my iOS device.