Omnibox UI Experiments: Add vertical margin variations to about:flags

components/omnibox/browser/omnibox_field_trial.h

Index: components/omnibox/browser/omnibox_field_trial.h
diff --git a/components/omnibox/browser/omnibox_field_trial.h b/components/omnibox/browser/omnibox_field_trial.h
index 2ff41730ad4f354098ebb40963a67a9c3b903033..1bff94e1f2aa754402e18bd36669526db08d2a47 100644
--- a/components/omnibox/browser/omnibox_field_trial.h
+++ b/components/omnibox/browser/omnibox_field_trial.h
@@ -32,6 +32,7 @@ extern const base::Feature kSearchProviderContextAllowHttpsUrls;
 extern const base::Feature kZeroSuggestRedirectToChrome;
 extern const base::Feature kZeroSuggestSwapTitleAndUrl;
 extern const base::Feature kDisplayTitleForCurrentUrl;
+extern const base::Feature kUIExperiments;
 }
 
 // The set of parameters customizing the HUP scoring.
@@ -495,6 +496,9 @@ class OmniboxFieldTrial {
   static const char kZeroSuggestRedirectToChromeServerAddressParam[];
   static const char kZeroSuggestRedirectToChromeAdditionalFieldsParam[];
 
+  // Parameter names used by UI experiments.
+  static const char kUIExperimentsVerticalMarginParam[];
+
   // The amount of time to wait before sending a new suggest request after the
   // previous one unless overridden by a field trial parameter.
   // Non-const because some unittests modify this value.