mash json pref store: Handle seeks in empty files on windows.

components/filesystem/public/cpp/prefs/filesystem_json_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 "components/filesystem/public/cpp/prefs/filesystem_json_pref_store.h"
 
 #include <stddef.h>
 
 #include <algorithm>
 #include <utility>
@@ skipping 410 matching lines @@
     mojo::Array<uint8_t> contents) {
   scoped_ptr<FilesystemJsonPrefStore::ReadResult> read_result(
       new FilesystemJsonPrefStore::ReadResult);
   // TODO(erg): Needs even better error handling.
   switch (err) {
     case FileError::IN_USE:
     case FileError::ACCESS_DENIED: {
       read_only_ = true;
       break;
     }
+    case FileError::FAILED:
     case FileError::NOT_FOUND: {
       // If the file just doesn't exist, maybe this is the first run. Just
       // don't pass a value.
       read_result->error = PREF_READ_ERROR_NO_FILE;
       break;
     }
     default: {
       int error_code;
       std::string error_msg;
       JSONStringValueDeserializer deserializer(base::StringPiece(
           reinterpret_cast<char*>(&contents.front()), contents.size()));
       read_result->value = deserializer.Deserialize(&error_code, &error_msg);
       read_result->error = HandleReadErrors(read_result->value.get());
     }
   }
 
   preferences_file_.reset();
 
   OnFileRead(std::move(read_result));
 }
 
 }  // namespace filesystem