[NTP4] Fix empty apps page crash.

chrome/browser/extensions/extension_sorting.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_EXTENSIONS_EXTENSION_SORTING_H_
 #define CHROME_BROWSER_EXTENSIONS_EXTENSION_SORTING_H_
 #pragma once
 
 #include <string>
 
@@ skipping 75 matching lines @@
 
   // Removes the ordinal values for an app.
   void ClearOrdinals(const std::string& extension_id);
 
   // Convert the page StringOrdinal value to its integer equivalent. This takes
   // O(# of apps) worst-case.
   int PageStringOrdinalAsInteger(const StringOrdinal& page_ordinal) const;
 
   // Converts the page index integer to its StringOrdinal equivalent. This takes
   // O(# of apps) worst-case.
-  StringOrdinal PageIntegerAsStringOrdinal(size_t page_index) const;
+  StringOrdinal PageIntegerAsStringOrdinal(size_t page_index);
 
  private:
   // Unit tests.
   friend class ExtensionSortingGetMinOrMaxAppLaunchOrdinalsOnPage;
   friend class ExtensionSortingInitializeWithNoApps;
   friend class ExtensionSortingPageOrdinalMapping;
 
   // An enum used by GetMinOrMaxAppLaunchOrdinalsOnPage to specify which
   // value should be returned.
   enum AppLaunchOrdinalReturn {MIN_ORDINAL, MAX_ORDINAL};
@@ skipping 15 matching lines @@
   // Migrates the app launcher and page index values.
   void MigrateAppIndex(const ExtensionPrefs::ExtensionIdSet& extension_ids);
 
   // Called to add a new mapping value for |extension_id| with a page ordinal
   // of |page_ordinal| and a app launch ordinal of |app_launch_ordinal|. This
   // works with valid and invalid StringOrdinals.
   void AddOrdinalMapping(const std::string& extension_id,
                          const StringOrdinal& page_ordinal,
                          const StringOrdinal& app_launch_ordinal);
 
+  // Ensures |ntp_ordinal_map_| is of |minimum_size| number of entries.
+  void CreateOrdinalsIfNecessary(size_t minimum_size);
+
   // Removes the mapping for |extension_id| with a page ordinal of
   // |page_ordinal| and a app launch ordinal of |app_launch_ordinal|. If there
   // is not matching map, nothing happens. This works with valid and invalid
   // StringOrdinals.
   void RemoveOrdinalMapping(const std::string& extension_id,
                             const StringOrdinal& page_ordinal,
                             const StringOrdinal& app_launch_ordinal);
 
   // Syncs the extension if needed. It is an error to call this if the
   // extension is not an application.
@@ skipping 17 matching lines @@
   // The StringOrdinal is the page ordinal and the AppLaunchOrdinalMap is the
   // contents of that page.
   typedef std::map<
       StringOrdinal, AppLaunchOrdinalMap, StringOrdinalLessThan> PageOrdinalMap;
   PageOrdinalMap ntp_ordinal_map_;
 
   DISALLOW_COPY_AND_ASSIGN(ExtensionSorting);
 };
 
 #endif  // CHROME_BROWSER_EXTENSIONS_EXTENSION_SORTING_H_