Assume all providers may give zero suggest responses.

chrome/browser/autocomplete/zero_suggest_provider.h

Index: chrome/browser/autocomplete/zero_suggest_provider.h
diff --git a/chrome/browser/autocomplete/zero_suggest_provider.h b/chrome/browser/autocomplete/zero_suggest_provider.h
index 17c23e1f31155c345a6196c0d4ffa18e3b28a921..36b73403f37a980e745b899221d2c98410e857d1 100644
--- a/chrome/browser/autocomplete/zero_suggest_provider.h
+++ b/chrome/browser/autocomplete/zero_suggest_provider.h
@@ -37,7 +37,7 @@ 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.
@@ -57,11 +57,12 @@ class ZeroSuggestProvider : public BaseSearchProvider,
   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;