Don't sync browser.show_home_button and homepage_is_newtabpage to mobile platforms.

chrome/browser/ui/browser_ui_prefs.cc

 // 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.
 
 #include "chrome/browser/ui/browser_ui_prefs.h"
 
 #include "build/build_config.h"
 #include "chrome/browser/first_run/first_run.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/common/pref_names.h"
@@ skipping 15 matching lines @@
   registry->RegisterBooleanPref(prefs::kAllowFileSelectionDialogs, true);
   registry->RegisterIntegerPref(prefs::kShowFirstRunBubbleOption,
                              first_run::FIRST_RUN_BUBBLE_DONT_SHOW);
 }
 
 void RegisterBrowserUserPrefs(user_prefs::PrefRegistrySyncable* registry) {
   registry->RegisterBooleanPref(
       prefs::kHomePageIsNewTabPage,
       true,
       user_prefs::PrefRegistrySyncable::SYNCABLE_PREF);
+#if defined(OS_IOS) || defined(OS_ANDROID)
+  uint32_t flags = PrefRegistry::NO_REGISTRATION_FLAGS;

[sky, 2016/06/23 15:49:33]

nit: please use a better name than flags, perhaps home_button_flags. Another
option is to move this to a function and change line 44 to GetHomeButtonFlags().

[melandory, 2016/06/25 01:24:50]

Done.

+#else
+  uint32_t flags = user_prefs::PrefRegistrySyncable::SYNCABLE_PREF;
+#endif
   registry->RegisterBooleanPref(
       prefs::kShowHomeButton,
       false,
-      user_prefs::PrefRegistrySyncable::SYNCABLE_PREF);
+      flags);
   registry->RegisterBooleanPref(
       prefs::kDeleteBrowsingHistory,
       true,
       user_prefs::PrefRegistrySyncable::SYNCABLE_PREF);
   registry->RegisterBooleanPref(
       prefs::kDeleteDownloadHistory,
       true,
       user_prefs::PrefRegistrySyncable::SYNCABLE_PREF);
   registry->RegisterBooleanPref(
       prefs::kDeleteCache,
@@ skipping 93 matching lines @@
   registry->RegisterBooleanPref(
       prefs::kHideFullscreenToolbar,
       false,
       user_prefs::PrefRegistrySyncable::SYNCABLE_PREF);
 #else
   registry->RegisterBooleanPref(prefs::kFullscreenAllowed, true);
 #endif
 }
 
 }  // namespace chrome