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 71 matching lines @@
                            DontInlineAutocompleteAsynchronously);
   FRIEND_TEST_ALL_PREFIXES(SearchProviderTest, NavigationInline);
   FRIEND_TEST_ALL_PREFIXES(SearchProviderTest, NavigationInlineDomainClassify);
   FRIEND_TEST_ALL_PREFIXES(SearchProviderTest, NavigationInlineSchemeSubstring);
   FRIEND_TEST_ALL_PREFIXES(SearchProviderTest, SuggestRelevanceExperiment);
   FRIEND_TEST_ALL_PREFIXES(SearchProviderTest, TestDeleteMatch);
   FRIEND_TEST_ALL_PREFIXES(SearchProviderTest, SuggestQueryUsesToken);
   FRIEND_TEST_ALL_PREFIXES(SearchProviderTest, SessionToken);
   FRIEND_TEST_ALL_PREFIXES(SearchProviderTest, AnswersCache);
   FRIEND_TEST_ALL_PREFIXES(SearchProviderTest, RemoveExtraAnswers);
+  FRIEND_TEST_ALL_PREFIXES(SearchProviderTest, DoesNotProvideOnFocus);
   FRIEND_TEST_ALL_PREFIXES(AutocompleteProviderTest, GetDestinationURL);
   FRIEND_TEST_ALL_PREFIXES(InstantExtendedPrefetchTest, ClearPrefetchedResults);
   FRIEND_TEST_ALL_PREFIXES(InstantExtendedPrefetchTest, SetPrefetchQuery);
 
   // Manages the providers (TemplateURLs) used by SearchProvider. Two providers
   // may be used:
   // . The default provider. This corresponds to the user's default search
   //   engine. This is always used, except for the rare case of no default
   //   engine.
   // . The keyword provider. This is used if the user has typed in a keyword.
@@ skipping 49 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 called_due_to_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_