Add a new entry to omnibox_event.proto to log specific type of contextual suggestions

components/omnibox/browser/autocomplete_match.h

Index: components/omnibox/browser/autocomplete_match.h
diff --git a/components/omnibox/browser/autocomplete_match.h b/components/omnibox/browser/autocomplete_match.h
index 9ab496c7dc665b0f6ba3e7c7b95271b882cc1e00..86ee897acd28e352df354f1135c3eff453703671 100644
--- a/components/omnibox/browser/autocomplete_match.h
+++ b/components/omnibox/browser/autocomplete_match.h
@@ -367,6 +367,12 @@ struct AutocompleteMatch {
   // Type of this match.
   Type type;
 
+  // Used to identify the specify type of the autocomplete match. For example,
+  // contextual zero suggest suggestions uses this field to record the specific
+  // suggestion types in order to assess the quality of multiple suggestion
+  // sources.
+  int specific_type_identifier = 0;
+
   // Set with a keyword provider match if this match can show a keyword hint.
   // For example, if this is a SearchProvider match for "www.amazon.com",
   // |associated_keyword| could be a KeywordProvider match for "amazon.com".