Explicitly check various sync_file_system classes live on the IO thread.

chrome/browser/sync_file_system/local/local_file_sync_status.h

 // Copyright 2013 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.
 
 #ifndef CHROME_BROWSER_SYNC_FILE_SYSTEM_LOCAL_LOCAL_FILE_SYNC_STATUS_H_
 #define CHROME_BROWSER_SYNC_FILE_SYSTEM_LOCAL_LOCAL_FILE_SYNC_STATUS_H_
 
 #include <stdint.h>
 
 #include <map>
 #include <set>
+#include <utility>
 
 #include "base/compiler_specific.h"
 #include "base/gtest_prod_util.h"
 #include "base/macros.h"
 #include "base/observer_list.h"
-#include "base/threading/non_thread_safe.h"
 #include "storage/browser/fileapi/file_system_url.h"
 
 namespace storage {
 class FileSystemURL;
 }
 
 namespace sync_file_system {
 
 // Represents local file sync status.
 // This class is supposed to run only on IO thread.
 //
 // This class manages two important synchronization flags: writing (counter)
 // and syncing (flag).  Writing counter keeps track of which URL is in
 // writing and syncing flag indicates which URL is in syncing.
 //
 // An entry can have multiple writers but sync is exclusive and cannot overwrap
 // with any writes or syncs.
-class LocalFileSyncStatus
-    : public base::NonThreadSafe {
+class LocalFileSyncStatus {
  public:
-  typedef std::pair<GURL, storage::FileSystemType> OriginAndType;
+  using OriginAndType = std::pair<GURL, storage::FileSystemType>;
 
   class Observer {
    public:
     Observer() {}
     virtual ~Observer() {}
     virtual void OnSyncEnabled(const storage::FileSystemURL& url) = 0;
     virtual void OnWriteEnabled(const storage::FileSystemURL& url) = 0;
 
    private:
     DISALLOW_COPY_AND_ASSIGN(Observer);
@@ skipping 26 matching lines @@
   // syncing nor writing).
   bool IsSyncable(const storage::FileSystemURL& url) const;
 
   void AddObserver(Observer* observer);
   void RemoveObserver(Observer* observer);
 
  private:
   FRIEND_TEST_ALL_PREFIXES(LocalFileSyncStatusTest, WritingOnPathsWithPeriod);
   FRIEND_TEST_ALL_PREFIXES(LocalFileSyncStatusTest, SyncingOnPathsWithPeriod);
 
-  typedef std::set<base::FilePath> PathSet;
-  typedef std::map<OriginAndType, PathSet> URLSet;
+  using PathSet = std::set<base::FilePath>;
+  using URLSet = std::map<OriginAndType, PathSet>;
 
-  typedef std::map<base::FilePath, int64_t> PathBucket;
-  typedef std::map<OriginAndType, PathBucket> URLBucket;
+  using PathBucket = std::map<base::FilePath, int64_t>;
+  using URLBucket = std::map<OriginAndType, PathBucket>;
 
   bool IsChildOrParentWriting(const storage::FileSystemURL& url) const;
   bool IsChildOrParentSyncing(const storage::FileSystemURL& url) const;
 
-  // If this count is non-zero positive there're ongoing write operations.
+  // If this count is non-zero, then there are ongoing write operations.
   URLBucket writing_;
 
   // If this flag is set sync process is running on the file.
   URLSet syncing_;
 
   base::ObserverList<Observer> observer_list_;
 
   DISALLOW_COPY_AND_ASSIGN(LocalFileSyncStatus);
 };
 
 }  // namespace sync_file_system
 
 #endif  // CHROME_BROWSER_SYNC_FILE_SYSTEM_LOCAL_LOCAL_FILE_SYNC_STATUS_H_