Assume all providers may give zero suggest responses.

chrome/browser/autocomplete/builtin_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_BUILTIN_PROVIDER_H_
 #define CHROME_BROWSER_AUTOCOMPLETE_BUILTIN_PROVIDER_H_
 
 #include <vector>
 
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
 #include "base/strings/string16.h"
 #include "components/omnibox/autocomplete_match.h"
 #include "components/omnibox/autocomplete_provider.h"
 
 // This is the provider for built-in URLs, such as about:settings and
 // chrome://version.
 class BuiltinProvider : public AutocompleteProvider {
  public:
   BuiltinProvider();
 
   // AutocompleteProvider:
-  void Start(const AutocompleteInput& input, bool minimal_changes) override;
+  void Start(const AutocompleteInput& input,
+             bool minimal_changes,
+             bool on_focus) override;
 
  private:
   ~BuiltinProvider() override;
 
   typedef std::vector<base::string16> Builtins;
 
   static const int kRelevance;
 
   void AddMatch(const base::string16& match_string,
                 const base::string16& inline_completion,
                 const ACMatchClassifications& styles);
 
   Builtins builtins_;
 
   DISALLOW_COPY_AND_ASSIGN(BuiltinProvider);
 };
 
 #endif  // CHROME_BROWSER_AUTOCOMPLETE_BUILTIN_PROVIDER_H_