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

components/metrics/proto/omnibox_event.proto

Index: components/metrics/proto/omnibox_event.proto
diff --git a/components/metrics/proto/omnibox_event.proto b/components/metrics/proto/omnibox_event.proto
index 0410d6cc0edfd97b55f6d4b7dec11a15de84dcee..c8d0ff834e059d31121ae6ef8dc012f33e0fdd91 100644
--- a/components/metrics/proto/omnibox_event.proto
+++ b/components/metrics/proto/omnibox_event.proto
@@ -177,7 +177,7 @@ message OmniboxEventProto {
   }
 
   // The result set displayed on the completion popup
-  // Next tag: 7
+  // Next tag: 8
   message Suggestion {
     // Where does this result come from?
     optional ProviderType provider = 1;
@@ -253,6 +253,11 @@ message OmniboxEventProto {
 
     // Whether this item is disabled in the UI (not clickable).
     optional bool is_disabled = 6;
+
+    // Used to identify the specific source / type of suggestion for suggestions
+    // provided by the suggest server.  For meaning of individual values, see
+    // the server-side enum.
+    optional int32 result_subtype_identifier = 7;
   }
   repeated Suggestion suggestion = 9;