[NTP4] Fix empty apps page crash.

chrome/browser/extensions/extension_sorting.h

Index: chrome/browser/extensions/extension_sorting.h
diff --git a/chrome/browser/extensions/extension_sorting.h b/chrome/browser/extensions/extension_sorting.h
index b0bf38a6079b5b7dbd76be2bab455b13a0d34a55..e0156b112437106d5131d1a948a3c58f8eb041c8 100644
--- a/chrome/browser/extensions/extension_sorting.h
+++ b/chrome/browser/extensions/extension_sorting.h
@@ -93,7 +93,7 @@ class ExtensionSorting {
 
   // 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.
@@ -129,6 +129,9 @@ class ExtensionSorting {
                          const StringOrdinal& page_ordinal,
                          const StringOrdinal& app_launch_ordinal);
 
+  // Ensures |ntp_ordinal_map_| is of |required_size| number of entries.
+  void CreateOrdinalsIfNecessary(size_t required_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