Remove migration of obsolete value for "session.restore_on_startup".

chrome/browser/prefs/session_startup_pref.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_PREFS_SESSION_STARTUP_PREF_H__
 #define CHROME_BROWSER_PREFS_SESSION_STARTUP_PREF_H__
 
 #include <vector>
 
 #include "url/gurl.h"
 
 class PrefService;
 class Profile;
 
 namespace user_prefs {
 class PrefRegistrySyncable;
 }
 
 // StartupPref specifies what should happen at startup for a specified profile.
 // StartupPref is stored in the preferences for a particular profile.
 struct SessionStartupPref {
   enum Type {
     // Indicates the user wants to open the New Tab page.
     DEFAULT,
 
-    // Deprecated. See comment in session_startup_pref.cc
-    HOMEPAGE,
-
     // Indicates the user wants to restore the last session.
     LAST,
 
     // Indicates the user wants to restore a specific set of URLs. The URLs
     // are contained in urls.
     URLS,
 
     // Number of values in this enum.
     TYPE_COUNT
   };
 
   // For historical reasons the enum and value registered in the prefs don't
   // line up. These are the values registered in prefs.
   // The values are also recorded in Settings.StartupPageLoadSettings histogram,
   // so make sure to update histograms.xml if you change these.
-  static const int kPrefValueHomePage = 0;  // Deprecated

[bartfab (slow), 2015/08/31 15:36:43]

+asvitkine@chromium.org Your advice is needed is needed here. The comment above
reminds us to update histograms.xml. The value 0 is currently documented there
as:

<int value="0" label="Open home page (unused)"/>

Should we remove this entry as it is truly unused now, or should we leave it so
that if some old or misconfigured client does report a value of 0, we can easily
see in the histogram what this used to refer to?

   static const int kPrefValueLast = 1;
   static const int kPrefValueURLs = 4;
   static const int kPrefValueNewTab = 5;
   static const int kPrefValueMax = 6;
 
   static void RegisterProfilePrefs(user_prefs::PrefRegistrySyncable* registry);
 
   // Returns the default value for |type|.
   static Type GetDefaultStartupType();
 
   // What should happen on startup for the specified profile.
   static void SetStartupPref(Profile* profile, const SessionStartupPref& pref);
   static void SetStartupPref(PrefService* prefs,
                              const SessionStartupPref& pref);
   static SessionStartupPref GetStartupPref(Profile* profile);
   static SessionStartupPref GetStartupPref(PrefService* prefs);
 
-  // If the user had the "restore on startup" property set to the deprecated
-  // "Open the home page" value, this migrates them to a value that will have
-  // the same effect.
-  static void MigrateIfNecessary(PrefService* prefs);
-
   // Whether the startup type and URLs are managed via policy.
   static bool TypeIsManaged(PrefService* prefs);
   static bool URLsAreManaged(PrefService* prefs);
 
   // Whether the startup type has not been overridden from its default.
   static bool TypeIsDefault(PrefService* prefs);
 
   // Converts an integer pref value to a SessionStartupPref::Type.
   static SessionStartupPref::Type PrefValueToType(int pref_value);
 
   explicit SessionStartupPref(Type type);
 
   ~SessionStartupPref();
 
   // What to do on startup.
   Type type;
 
   // The URLs to restore. Only used if type == URLS.
   std::vector<GURL> urls;
 };
 
 #endif  // CHROME_BROWSER_PREFS_SESSION_STARTUP_PREF_H__