Replace deprecated base::NonThreadSafe in extensions in favor of SequenceChecker.

extensions/browser/value_store/value_store_frontend.h

 // Copyright 2014 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 EXTENSIONS_BROWSER_VALUE_STORE_VALUE_STORE_FRONTEND_H_
 #define EXTENSIONS_BROWSER_VALUE_STORE_VALUE_STORE_FRONTEND_H_
 
 #include <memory>
 #include <string>
 
 #include "base/callback.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/weak_ptr.h"
-#include "base/threading/non_thread_safe.h"
+#include "base/sequence_checker.h"
 #include "base/values.h"
 #include "extensions/browser/value_store/value_store.h"
 
 namespace extensions {
 class ValueStoreFactory;
 }  // namespace extensions
 
 // A frontend for a LeveldbValueStore, for use on the UI thread.

[Devlin, 2017/05/30 19:06:47]

Since this is only designed to be used on the UI thread, probably ThreadChecker.

[gab, 2017/05/31 17:52:28]

I don't see thread-affinity requirements in ValueStoreFrontend's design?
Anyways, added BrowserThread::UI checks for now to match current API comment.

-class ValueStoreFrontend
-    : public base::SupportsWeakPtr<ValueStoreFrontend>,
-      public base::NonThreadSafe {
+class ValueStoreFrontend : public base::SupportsWeakPtr<ValueStoreFrontend> {
  public:
   // The kind of extensions data stored in a backend.
   enum class BackendType { RULES, STATE };
 
   typedef base::Callback<void(std::unique_ptr<base::Value>)> ReadCallback;
 
   ValueStoreFrontend(
       const scoped_refptr<extensions::ValueStoreFactory>& store_factory,
       BackendType backend_type);
   ~ValueStoreFrontend();
 
   // Retrieves a value from the database asynchronously, passing a copy to
   // |callback| when ready. NULL is passed if no matching entry is found.
   void Get(const std::string& key, const ReadCallback& callback);
 
   // Sets a value with the given key.
   void Set(const std::string& key, std::unique_ptr<base::Value> value);
 
   // Removes the value with the given key.
   void Remove(const std::string& key);
 
  private:
   class Backend;
 
   // A helper class to manage lifetime of the backing ValueStore, which lives
   // on the FILE thread.
   scoped_refptr<Backend> backend_;
 
+  SEQUENCE_CHECKER(sequence_checker_);
+
   DISALLOW_COPY_AND_ASSIGN(ValueStoreFrontend);
 };
 
 #endif  // EXTENSIONS_BROWSER_VALUE_STORE_VALUE_STORE_FRONTEND_H_