[omnibox] Add flag OmniboxZeroSuggestionsOnSERP

This flag isn't strictly speaking necessary, since we have the existing
OmniboxOnFocusSuggestions flag that can be configured in about:flags.

But this new separate flag does allow users to put themselves into a
field trial forcing group, which could be useful if we decide to change
the server-side variation ids.

Bug: 991031
Change-Id: Ie7887dd9fff86bdcca07d870d6da3738a5d58f33
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1815080
Commit-Queue: Tommy Li <[email protected]>
Reviewed-by: Justin Donnelly <[email protected]>
Cr-Commit-Position: refs/heads/master@{#699111}
diff --git a/components/omnibox/common/omnibox_features.cc b/components/omnibox/common/omnibox_features.cc
index 6c3ff55..696ccbd 100644
--- a/components/omnibox/common/omnibox_features.cc
+++ b/components/omnibox/common/omnibox_features.cc
@@ -297,6 +297,10 @@
 const base::Feature kZeroSuggestionsOnNTPRealbox{
     "OmniboxZeroSuggestionsOnNTPRealbox", base::FEATURE_DISABLED_BY_DEFAULT};
 
+// Allow on-focus query refinements to be shown on the default SERP.
+const base::Feature kZeroSuggestionsOnSERP{"OmniboxZeroSuggestionsOnSERP",
+                                           base::FEATURE_ENABLED_BY_DEFAULT};
+
 // Feature to provide non personalized head search suggestion from a compact
 // on device model.
 const base::Feature kOnDeviceHeadProvider{"OmniboxOnDeviceHeadProvider",