[Sync] Allow sync start without sign-in if the local sync backend is on.

chrome/browser/prefs/chrome_command_line_pref_store.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/prefs/chrome_command_line_pref_store.h"
 
 #include <stddef.h>
 
 #include <string>
 #include <utility>
@@ skipping 65 matching lines @@
          prefs::kAllowCrossOriginAuthPrompt, true},
         {switches::kDisablePrintPreview, prefs::kPrintPreviewDisabled, true},
 #if defined(OS_CHROMEOS)
         {chromeos::switches::kEnableTouchpadThreeFingerClick,
          prefs::kEnableTouchpadThreeFingerClick, true},
         {switches::kEnableUnifiedDesktop,
          prefs::kUnifiedDesktopEnabledByDefault, true},
 #endif
         {switches::kUnsafePacUrl, prefs::kPacHttpsUrlStrippingEnabled, false},
         {switches::kEnableLocalSyncBackend,
-         syncer::prefs::kEnableLocalSyncBackend, false},
+         syncer::prefs::kEnableLocalSyncBackend, true},
 };
 
 const CommandLinePrefStore::SwitchToPreferenceMapEntry
     ChromeCommandLinePrefStore::integer_switch_map_[] = {
       { switches::kDiskCacheSize, prefs::kDiskCacheSize },
       { switches::kMediaCacheSize, prefs::kMediaCacheSize },
     };
 
 ChromeCommandLinePrefStore::ChromeCommandLinePrefStore(
     const base::CommandLine* command_line)
@@ skipping 70 matching lines @@
   }
 }
 
 void ChromeCommandLinePrefStore::ApplyBackgroundModeSwitches() {
   if (command_line()->HasSwitch(switches::kDisableExtensions)) {
     SetValue(prefs::kBackgroundModeEnabled,
              base::MakeUnique<base::FundamentalValue>(false),
              WriteablePrefStore::DEFAULT_PREF_WRITE_FLAGS);
   }
 }