Assume all providers may give zero suggest responses.

chrome/browser/autocomplete/bookmark_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.
 
 #ifndef CHROME_BROWSER_AUTOCOMPLETE_BOOKMARK_PROVIDER_H_
 #define CHROME_BROWSER_AUTOCOMPLETE_BOOKMARK_PROVIDER_H_
 
 #include <string>
 
 #include "components/omnibox/autocomplete_input.h"
@@ skipping 16 matching lines @@
 //
 // TODO(mrossetti): Propose a way to coordinate with the HQP the taking of typed
 // and visit counts and last visit dates, etc. into consideration while scoring.
 class BookmarkProvider : public AutocompleteProvider {
  public:
   explicit BookmarkProvider(Profile* profile);
 
   // When |minimal_changes| is true short circuit any additional searching and
   // leave the previous matches for this provider unchanged, otherwise perform
   // a complete search for |input| across all bookmark titles.
-  void Start(const AutocompleteInput& input, bool minimal_changes) override;
+  void Start(const AutocompleteInput& input,
+             bool minimal_changes,
+             bool on_focus) override;
 
   // Sets the BookmarkModel for unit tests.
   void set_bookmark_model_for_testing(BookmarkModel* bookmark_model) {
     bookmark_model_ = bookmark_model;
   }
 
  private:
   FRIEND_TEST_ALL_PREFIXES(BookmarkProviderTest, InlineAutocompletion);
 
   ~BookmarkProvider() override;
@@ skipping 24 matching lines @@
   Profile* profile_;
   BookmarkModel* bookmark_model_;
 
   // Languages used during the URL formatting.
   std::string languages_;
 
   DISALLOW_COPY_AND_ASSIGN(BookmarkProvider);
 };
 
 #endif  // CHROME_BROWSER_AUTOCOMPLETE_BOOKMARK_PROVIDER_H_