*DRAFT* Move MediaDeviceIDSalt from chrome/ to components/ and use it in Android WebView.

chrome/browser/media/media_device_id_salt.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_MEDIA_MEDIA_DEVICE_ID_SALT_H_
-#define CHROME_BROWSER_MEDIA_MEDIA_DEVICE_ID_SALT_H_
-
-#include <string>
-
-#include "base/macros.h"
-#include "base/memory/ref_counted.h"
-#include "components/pref_registry/pref_registry_syncable.h"
-#include "components/prefs/pref_member.h"
-
-class PrefService;
-
-// MediaDeviceIDSalt is responsible for creating and retrieving a salt string
-// that is used for creating MediaSource IDs that can be cached by a web
-// service. If the cache is cleared, the  MediaSourceIds are invalidated.
-//
-// The class is reference counted so that it can be used in the
-// callback returned by ResourceContext::GetMediaDeviceIDSalt.
-class MediaDeviceIDSalt : public base::RefCountedThreadSafe<MediaDeviceIDSalt> {
- public:
-  MediaDeviceIDSalt(PrefService* pref_service, bool incognito);
-  void ShutdownOnUIThread();
-
-  std::string GetSalt() const;
-
-  static void RegisterProfilePrefs(user_prefs::PrefRegistrySyncable* registry);
-  static void Reset(PrefService* pref_service);
-
- private:
-  friend class base::RefCountedThreadSafe<MediaDeviceIDSalt>;
-  ~MediaDeviceIDSalt();
-
-  // |incognito_salt_| is initialized in ctor on UI thread but only read
-  //  on the IO thread.
-  std::string incognito_salt_;
-  mutable StringPrefMember media_device_id_salt_;
-
-  DISALLOW_COPY_AND_ASSIGN(MediaDeviceIDSalt);
-};
-
-#endif  // CHROME_BROWSER_MEDIA_MEDIA_DEVICE_ID_SALT_H_