Don't sync pref which controls the password manager to mobile.

components/password_manager/core/browser/password_manager.cc

Index: components/password_manager/core/browser/password_manager.cc
diff --git a/components/password_manager/core/browser/password_manager.cc b/components/password_manager/core/browser/password_manager.cc
index 990424c8882682d771d002bd5bb330af3d1d9d19..932ce8e6ed08774701cd4ac6ec9488aedf08d40f 100644
--- a/components/password_manager/core/browser/password_manager.cc
+++ b/components/password_manager/core/browser/password_manager.cc
@@ -135,10 +135,13 @@ bool ContainsAndroidCredentials(
 // static
 void PasswordManager::RegisterProfilePrefs(
     user_prefs::PrefRegistrySyncable* registry) {
-  registry->RegisterBooleanPref(
-      prefs::kPasswordManagerSavingEnabled,
-      true,
-      user_prefs::PrefRegistrySyncable::SYNCABLE_PREF);
+#if defined(OS_IOS) || defined(OS_ANDROID)
+  uint32_t flags = PrefRegistry::NO_REGISTRATION_FLAGS;
+#else
+  uint32_t flags = user_prefs::PrefRegistrySyncable::SYNCABLE_PREF;
+#endif
+  registry->RegisterBooleanPref(prefs::kPasswordManagerSavingEnabled, true,
+                                flags);
   registry->RegisterBooleanPref(
       prefs::kCredentialsEnableService, true,
       user_prefs::PrefRegistrySyncable::SYNCABLE_PRIORITY_PREF);