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

chrome/browser/ui/browser_ui_prefs.cc

Index: chrome/browser/ui/browser_ui_prefs.cc
diff --git a/chrome/browser/ui/browser_ui_prefs.cc b/chrome/browser/ui/browser_ui_prefs.cc
index e14a72b70c0c762a1a1a713ab0c40920b62e6f59..071d9a0358bd887b86387679faa61fa775b9efe6 100644
--- a/chrome/browser/ui/browser_ui_prefs.cc
+++ b/chrome/browser/ui/browser_ui_prefs.cc
@@ -33,10 +33,15 @@ void RegisterBrowserUserPrefs(user_prefs::PrefRegistrySyncable* registry) {
       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,