Assume all providers may give zero suggest responses.

chrome/browser/autocomplete/history_url_provider.h

Index: chrome/browser/autocomplete/history_url_provider.h
diff --git a/chrome/browser/autocomplete/history_url_provider.h b/chrome/browser/autocomplete/history_url_provider.h
index 91a97cacb6dc79e400e5a9e51c123582918d2949..fe2c7a8df8cac1ef198d196a4ebb41720d94dcdc 100644
--- a/chrome/browser/autocomplete/history_url_provider.h
+++ b/chrome/browser/autocomplete/history_url_provider.h
@@ -194,7 +194,8 @@ class HistoryURLProvider : public HistoryProvider {
 
   // HistoryProvider:
   virtual void Start(const AutocompleteInput& input,
-                     bool minimal_changes) override;
+                     bool minimal_changes,
+                     bool on_focus) override;
   virtual void Stop(bool clear_cached_results) override;
 
   // Returns a match representing a navigation to |destination_url| given user