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

components/sync/base/sync_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 "components/sync/base/sync_prefs.h"
 
 #include "base/base64.h"
+#include "base/files/file_path.h"
 #include "base/logging.h"
+#include "base/path_service.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/values.h"
 #include "components/pref_registry/pref_registry_syncable.h"
 #include "components/prefs/pref_service.h"
 #include "components/sync/base/pref_names.h"
 
 namespace syncer {
 
 SyncPrefObserver::~SyncPrefObserver() {}
 
@@ skipping 527 matching lines @@
   if (base::Base64Decode(encoded, &decoded)) {
     nigori_specifics->ParseFromString(decoded);
   }
 }
 
 bool SyncPrefs::IsLocalSyncEnabled() const {
   return pref_service_->GetBoolean(prefs::kEnableLocalSyncBackend);
 }
 
 base::FilePath SyncPrefs::GetLocalSyncBackendDir() const {
-  return pref_service_->GetFilePath(prefs::kLocalSyncBackendDir);
+  base::FilePath local_sync_backend_folder =
+      pref_service_->GetFilePath(prefs::kLocalSyncBackendDir);
+
+#if defined(OS_WIN)
+  if (local_sync_backend_folder.empty()) {
+    // TODO(pastarmovj): Add DIR_ROAMING_USER_DATA to PathService to simplify
+    // this code and move the logic in its right place. See crbug/657810.
+    CHECK(
+        base::PathService::Get(base::DIR_APP_DATA, &local_sync_backend_folder));
+    local_sync_backend_folder =
+        local_sync_backend_folder.Append(FILE_PATH_LITERAL("Chrome/User Data"));
+  }
+#endif  // defined(OS_WIN)
+  return local_sync_backend_folder;
 }
 
 }  // namespace syncer