[omnibox] Support DemoteByTypeRule associated with a feature.

Previously, the DemoteByTypeRule was only usable if the params were set in the
OmniboxBundledExperimentV1 study. With this CL, a group in any study that
enables the OmniboxDemoteByType feature will also be able to set the params.

Bug: 264066
Change-Id: I7f0695f4cb71e46a7a533d240db2e91f105cda03
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1903665Reviewed-by: Tommy Li <tommycli@chromium.org>
Commit-Queue: manuk hovanesian <manukh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#713913}

components/omnibox/browser/omnibox_field_trial.cc

@@ -281,9 +281,19 @@ void OmniboxFieldTrial::GetDemotionsByType(
     OmniboxEventProto::PageClassification current_page_classification,
     DemotionMultipliers* demotions_by_type) {
   demotions_by_type->clear();
+
+  // Explicitly check whether the feature is enabled before calling
+  // |GetValueForRuleInContextByFeature| because it is possible for
+  // |GetValueForRuleInContextByFeature| to return an empty string even if the
+  // feature is enabled, and we don't want to fallback to
+  // |GetValueForRuleInContext| in this case.
   std::string demotion_rule =
-      OmniboxFieldTrial::internal::GetValueForRuleInContext(
-          kDemoteByTypeRule, current_page_classification);
+      base::FeatureList::IsEnabled(omnibox::kOmniboxDemoteByType)
+          ? OmniboxFieldTrial::internal::GetValueForRuleInContextByFeature(
+                omnibox::kOmniboxDemoteByType, kDemoteByTypeRule,
+                current_page_classification)
+          : OmniboxFieldTrial::internal::GetValueForRuleInContext(
+                kDemoteByTypeRule, current_page_classification);
   // If there is no demotion rule for this context, then use the default
   // value for that context.
   if (demotion_rule.empty()) {

components/omnibox/common/omnibox_features.cc

@@ -288,6 +288,12 @@ const base::Feature kOmniboxPreserveDefaultMatchAgainstAsyncUpdate{
     "OmniboxPreserveDefaultMatchAgainstAsyncUpdate",
     base::FEATURE_DISABLED_BY_DEFAULT};
 
+// Demotes the relevance scores when comparing suggestions based on the
+// suggestion's |AutocompleteMatchType| and the user's |PageClassification|.
+// This feature's main job is to contain the DemoteByType parameter.
+const base::Feature kOmniboxDemoteByType{"OmniboxDemoteByType",
+                                         base::FEATURE_DISABLED_BY_DEFAULT};
+
 // Feature to configure on-focus suggestions provided by ZeroSuggestProvider.
 // This feature's main job is to contain some field trial parameters such as:
 //  - "ZeroSuggestVariant" configures the per-page-classification mode of

components/omnibox/common/omnibox_features.h

@@ -53,6 +53,7 @@ extern const base::Feature kDebounceDocumentProvider;
 // TODO(tommycli): There are more flags above that belong in this category.
 extern const base::Feature kOmniboxPreserveDefaultMatchScore;
 extern const base::Feature kOmniboxPreserveDefaultMatchAgainstAsyncUpdate;
+extern const base::Feature kOmniboxDemoteByType;
 
 // On-Focus Suggestions a.k.a. ZeroSuggest.
 extern const base::Feature kOnFocusSuggestions;