Assume all providers may give zero suggest responses.

chrome/browser/autocomplete/autocomplete_controller.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CHROME_BROWSER_AUTOCOMPLETE_AUTOCOMPLETE_CONTROLLER_H_
 #define CHROME_BROWSER_AUTOCOMPLETE_AUTOCOMPLETE_CONTROLLER_H_
 
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
 #include "base/gtest_prod_util.h"
@@ skipping 63 matching lines @@
   void Start(const AutocompleteInput& input);
 
   // Cancels the current query, ensuring there will be no future notifications
   // fired.  If new matches have come in since the most recent notification was
   // fired, they will be discarded.
   //
   // If |clear_result| is true, the controller will also erase the result set.
   void Stop(bool clear_result);
 
   // Called when the omnibox is focused while no existing user input is in
-  // progress.  This is used to trigger any providers which want to provide
-  // matches in response to focus.  See
-  // AutocompleteProvider::ProvidesMatchesOnOmniboxFocus().
+  // progress.  This is used to call Start() on all providers with
+  // |called_due_to_focus| parameter set to check if they want to provide
+  // on focus matches.
   void OnOmniboxFocused(const AutocompleteInput& input);
 
   // Asks the relevant provider to delete |match|, and ensures observers are
   // notified of resulting changes immediately.  This should only be called when
   // no query is running.
   void DeleteMatch(const AutocompleteMatch& match);
 
   // Removes any entries that were copied from the last result. This is used by
   // the popup to ensure it's not showing an out-of-date query.
   void ExpireCopiedEntries();
@@ skipping 153 matching lines @@
   // Are we in Start()? This is used to avoid updating |result_| and sending
   // notifications until Start() has been invoked on all providers.
   bool in_start_;
 
   TemplateURLService* template_url_service_;
 
   DISALLOW_COPY_AND_ASSIGN(AutocompleteController);
 };
 
 #endif  // CHROME_BROWSER_AUTOCOMPLETE_AUTOCOMPLETE_CONTROLLER_H_