Assume all providers may give zero suggest responses.

components/omnibox/keyword_provider.h

 // Copyright 2014 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 keyword autocomplete provider. The keyword provider
 // is responsible for remembering/suggesting user "search keyword queries"
 // (e.g.  "imdb Godzilla") and then fixing them up into valid URLs.  An
 // instance of it gets created and managed by the autocomplete controller.
 // KeywordProvider uses a TemplateURLService to find the set of keywords.
 
@@ skipping 76 matching lines @@
   // TemplateURLModel::CleanUserInputKeyword()) to an enabled, substituting
   // keyword, returns that keyword; returns the empty string otherwise.
   base::string16 GetKeywordForText(const base::string16& text) const;
 
   // Creates a fully marked-up AutocompleteMatch for a specific keyword.
   AutocompleteMatch CreateVerbatimMatch(const base::string16& text,
                                         const base::string16& keyword,
                                         const AutocompleteInput& input);
 
   // 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;
 
  private:
   friend class KeywordExtensionsDelegateImpl;
 
   ~KeywordProvider() override;
 
   // Extracts the keyword from |input| into |keyword|. Any remaining characters
   // after the keyword are placed in |remaining_input|. Returns true if |input|
   // is valid and has a keyword. This makes use of SplitKeywordFromInput to
@@ skipping 40 matching lines @@
   TemplateURLService* model_;
 
   // Delegate to handle the extensions-only logic for KeywordProvider.
   // NULL when extensions are not enabled. May be NULL for tests.
   scoped_ptr<KeywordExtensionsDelegate> extensions_delegate_;
 
   DISALLOW_COPY_AND_ASSIGN(KeywordProvider);
 };
 
 #endif  // COMPONENTS_OMNIBOX_KEYWORD_PROVIDER_H_