Clean up threading model of external extension providers

chrome/browser/extensions/stateful_external_extension_provider.h

-// Copyright (c) 2009 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_EXTENSIONS_STATEFUL_EXTERNAL_EXTENSION_PROVIDER_H_
-#define CHROME_BROWSER_EXTENSIONS_STATEFUL_EXTERNAL_EXTENSION_PROVIDER_H_
-#pragma once
-
-#include "chrome/browser/extensions/external_extension_provider.h"
-
-class DictionaryValue;
-class ValueSerializer;
-class Version;
-
-// A specialization of the ExternalExtensionProvider that stores the registered
-// external extensions in a dictionary. This dictionary (|prefs_|) will be used
-// by HasExtension() and GetExtensionDetails() to return information about the
-// stored external extensions. It is the responsibility of specialized
-// subclasses to initialize this internal dictionary.
-// This provider can provide external extensions from two sources: crx files
-// and udpate URLs. The locations that the provider will report for these
-// are specified at the constructor.
-// Instances of this class are expected to be created and destroyed on the UI
-// thread and they are expecting public method calls from the FILE thread.
-class StatefulExternalExtensionProvider : public ExternalExtensionProvider {
- public:
-  // Initialize the location for external extensions originating from crx
-  // files: |crx_location|, and originating from update URLs:
-  // |download_location|. If either of the origins is not supported by this
-  // provider, then it should be initialized as Extensions::INVALID.
-  StatefulExternalExtensionProvider(
-      Extension::Location crx_location,
-      Extension::Location download_location);
-  virtual ~StatefulExternalExtensionProvider();
-
-  // ExternalExtensionProvider implementation:
-  virtual void VisitRegisteredExtension(Visitor* visitor) const;
-
-  virtual bool HasExtension(const std::string& id) const;
-
-  virtual bool GetExtensionDetails(const std::string& id,
-                                   Extension::Location* location,
-                                   scoped_ptr<Version>* version) const;
- protected:
-  // Location for external extensions that are provided by this provider from
-  // local crx files.
-  const Extension::Location crx_location_;
-  // Location for external extensions that are provided by this provider from
-  // update URLs.
-  const Extension::Location download_location_;
-
-  // Stores the dictionary of external extensions internally. Takes ownership
-  // of |prefs|.
-  void set_prefs(DictionaryValue* prefs);
-
- private:
-  // Dictionary of the external extensions that are provided by this provider.
-  scoped_ptr<DictionaryValue> prefs_;
-};
-
-#endif  // CHROME_BROWSER_EXTENSIONS_STATEFUL_EXTERNAL_EXTENSION_PROVIDER_H_