Screenshots of CL here: https://codereview.chromium.org/2873423002/

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The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/a5a538f9d1c209828582674ff09a11fe12dce47c

commit a5a538f9d1c209828582674ff09a11fe12dce47c
Author: tommycli <tommycli@chromium.org>
Date: Mon May 15 19:09:38 2017

Omnibox UI Experiments: Add flag to change max autocomplete matches.

Adds an about:flag to change the maximum number of autocomplete matches
total across all providers.

BUG= 720166 

Review-Url: https://codereview.chromium.org/2873423002
Cr-Commit-Position: refs/heads/master@{#471855}

[modify] https://crrev.com/a5a538f9d1c209828582674ff09a11fe12dce47c/chrome/browser/about_flags.cc
[modify] https://crrev.com/a5a538f9d1c209828582674ff09a11fe12dce47c/chrome/browser/flag_descriptions.cc
[modify] https://crrev.com/a5a538f9d1c209828582674ff09a11fe12dce47c/chrome/browser/flag_descriptions.h
[modify] https://crrev.com/a5a538f9d1c209828582674ff09a11fe12dce47c/chrome/browser/ui/views/omnibox/omnibox_popup_contents_view.cc
[modify] https://crrev.com/a5a538f9d1c209828582674ff09a11fe12dce47c/components/omnibox/browser/autocomplete_result.cc
[modify] https://crrev.com/a5a538f9d1c209828582674ff09a11fe12dce47c/components/omnibox/browser/autocomplete_result.h
[modify] https://crrev.com/a5a538f9d1c209828582674ff09a11fe12dce47c/components/omnibox/browser/omnibox_field_trial.cc
[modify] https://crrev.com/a5a538f9d1c209828582674ff09a11fe12dce47c/components/omnibox/browser/omnibox_field_trial.h
[modify] https://crrev.com/a5a538f9d1c209828582674ff09a11fe12dce47c/components/omnibox/browser/search_provider.cc
[modify] https://crrev.com/a5a538f9d1c209828582674ff09a11fe12dce47c/tools/metrics/histograms/enums.xml

Could you add the name of the flag, relevant parameters, or other testing instructions to this bug? Thanks!

Flag at: chrome://flags/#omnibox-ui-max-autocomplete-matches

1. Go to chrome://flags/#omnibox-ui-max-autocomplete-matches
2. Change the select box to the number of matches desired. Disabled, Enabled, or Default all trigger the default behavior.
3. Confirm restarting Chrome.
4. Type something into the omnibox.
5. Observe changed number of max matches.

This is a very useful feature, especially for users with big displays.

I think the ability to customize the number of matches could be and should be exposed in a more natural way, for example, as a button in the suggest dropdown like "Show more". Pressing the button would reveal "Show less" and "Remember". Of course the buttons could be simply icons e.g. + —. Or maybe a number input field with ▲▼ spinners.