Assume all providers may give zero suggest responses.

chrome/browser/autocomplete/zero_suggest_provider.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.
 //
 // This file contains the zero-suggest autocomplete provider. This experimental
 // provider is invoked when the user focuses in the omnibox prior to editing,
 // and generates search query suggestions based on the current URL.
 
 #ifndef CHROME_BROWSER_AUTOCOMPLETE_ZERO_SUGGEST_PROVIDER_H_
 #define CHROME_BROWSER_AUTOCOMPLETE_ZERO_SUGGEST_PROVIDER_H_
@@ skipping 19 matching lines @@
 namespace net {
 class URLFetcher;
 }
 
 namespace user_prefs {
 class PrefRegistrySyncable;
 }
 
 // Autocomplete provider for searches based on the current URL.
 //
-// The controller will call ProvidesMatchesOnOmniboxFocus when the user focuses
+// The controller will call Start() with |on_focus| set when the user focuses
 // the omnibox. After construction, the autocomplete controller repeatedly calls
 // Start() with some user input, each time expecting to receive an updated set
 // of matches.
 //
 // TODO(jered): Consider deleting this class and building this functionality
 // into SearchProvider after dogfood and after we break the association between
 // omnibox text and suggestions.
 class ZeroSuggestProvider : public BaseSearchProvider,
                             public net::URLFetcherDelegate {
  public:
   // Creates and returns an instance of this provider.
   static ZeroSuggestProvider* Create(AutocompleteProviderListener* listener,
                                      TemplateURLService* template_url_service,
                                      Profile* profile);
 
   // Registers a preference used to cache zero suggest results.
   static void RegisterProfilePrefs(user_prefs::PrefRegistrySyncable* registry);
 
   // AutocompleteProvider:
-  void Start(const AutocompleteInput& input, bool minimal_changes) override;
+  void Start(const AutocompleteInput& input,
+             bool minimal_changes,
+             bool called_due_to_focus) override;
   void Stop(bool clear_cached_results) override;
   void DeleteMatch(const AutocompleteMatch& match) override;
   void AddProviderInfo(ProvidersInfo* provider_info) const override;
-  bool ProvidesMatchesOnOmniboxFocus() const override;
 
   // Sets |field_trial_triggered_| to false.
   void ResetSession() override;
 
  private:
   ZeroSuggestProvider(AutocompleteProviderListener* listener,
                       TemplateURLService* template_url_service,
                       Profile* profile);
 
   ~ZeroSuggestProvider() override;
@@ skipping 86 matching lines @@
   // Whether we are waiting for a most visited visited urls callback to run.
   bool waiting_for_most_visited_urls_request_;
 
   // For callbacks that may be run after destruction.
   base::WeakPtrFactory<ZeroSuggestProvider> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(ZeroSuggestProvider);
 };
 
 #endif  // CHROME_BROWSER_AUTOCOMPLETE_ZERO_SUGGEST_PROVIDER_H_