Skip migrating for default shown sections prefs.

chrome/browser/dom_ui/shown_sections_handler.cc

 // Copyright (c) 2010 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.
 
 #include "chrome/browser/dom_ui/shown_sections_handler.h"
 
 #include "base/callback.h"
 #include "base/command_line.h"
 #include "base/string_number_conversions.h"
 #include "base/values.h"
@@ skipping 88 matching lines @@
                                     APPS | MINIMIZED_THUMB | MINIMIZED_RECENT);
 #else
   pref_service->RegisterIntegerPref(prefs::kNTPShownSections, THUMB);
 #endif
 }
 
 // static
 void ShownSectionsHandler::MigrateUserPrefs(PrefService* pref_service,
                                             int old_pref_version,
                                             int new_pref_version) {
+  // Nothing to migrate for default kNTPShownSections value.
+  const PrefService::Preference* shown_sections_pref =
+      pref_service->FindPreference(prefs::kNTPShownSections);
+  if (shown_sections_pref->IsDefaultValue())
+    return;
+
   bool changed = false;
   int shown_sections = pref_service->GetInteger(prefs::kNTPShownSections);
 
   if (old_pref_version < 3) {
     // In version 3, we went from being able to show multiple sections to being
     // able to show only one expanded at a time. The only two expandable
     // sections are APPS and THUMBS.
     if (shown_sections & APPS)
       shown_sections = APPS;
     else
@@ skipping 17 matching lines @@
 
     // Hide any open sections.
     mode &= ~ALL_SECTIONS_MASK;
 
     // Show the apps section.
     mode |= APPS;
 
     prefs->SetInteger(prefs::kNTPShownSections, mode);
   }
 }