Omnibox UI Experiments: Add Vertical Layout experiment (title-on-top).

This is a minimal Views-only patch that renders the title above the
origin. It doesn't change any styling yet, nor does it touch Cocoa.

Those will be in followup CLs.

BUG=725599

Review-Url: https://codereview.chromium.org/2901953002
Cr-Commit-Position: refs/heads/master@{#475119}
diff --git a/chrome/browser/about_flags.cc b/chrome/browser/about_flags.cc
index 588d5e6..bb25ae82 100644
--- a/chrome/browser/about_flags.cc
+++ b/chrome/browser/about_flags.cc
@@ -2967,6 +2967,11 @@
          kOmniboxUIMaxAutocompleteMatchesVariations,
          "OmniboxUIMaxAutocompleteVariations")},
 
+    {"omnibox-ui-vertical-layout",
+     flag_descriptions::kOmniboxUIVerticalLayoutName,
+     flag_descriptions::kOmniboxUIVerticalLayoutDescription, kOsDesktop,
+     FEATURE_VALUE_TYPE(omnibox::kUIExperimentVerticalLayout)},
+
     {"omnibox-ui-vertical-margin",
      flag_descriptions::kOmniboxUIVerticalMarginName,
      flag_descriptions::kOmniboxUIVerticalMarginDescription, kOsDesktop,