Assume all providers may give zero suggest responses.

components/omnibox/search_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 Search autocomplete provider.  This provider is
 // responsible for all autocomplete entries that start with "Search <engine>
 // for ...", including searching for the current input string, search
 // history, and search suggestions.  An instance of it gets created and
 // managed by the autocomplete controller.
 
@@ skipping 140 matching lines @@
       bool prefer_keyword);
 
   // A helper function for UpdateAllOldResults().
   static void UpdateOldResults(bool minimal_changes,
                                SearchSuggestionParser::Results* results);
 
   // Returns the first match in |matches| which might be chosen as default.
   static ACMatches::iterator FindTopMatch(ACMatches* matches);
 
   // AutocompleteProvider:
-  void Start(const AutocompleteInput& input, bool minimal_changes) override;
+  void Start(const AutocompleteInput& input,
+             bool minimal_changes,
+             bool on_focus) override;
   void Stop(bool clear_cached_results) override;
 
   // BaseSearchProvider:
   const TemplateURL* GetTemplateURL(bool is_keyword) const override;
   const AutocompleteInput GetInput(bool is_keyword) const override;
   bool ShouldAppendExtraParams(
       const SearchSuggestionParser::SuggestResult& result) const override;
   void RecordDeletionResult(bool success) override;
 
   // net::URLFetcherDelegate:
@@ skipping 222 matching lines @@
   base::TimeTicks token_expiration_time_;
 
   // Answers prefetch management.
   AnswersCache answers_cache_;  // Cache for last answers seen.
   AnswersQueryData prefetch_data_;  // Data to use for query prefetching.
 
   DISALLOW_COPY_AND_ASSIGN(SearchProvider);
 };
 
 #endif  // COMPONENTS_OMNIBOX_SEARCH_PROVIDER_H_