Revert of Make default media device ID salts random by default

chrome/browser/media/media_device_id_salt.cc

 // 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.
 #include "chrome/browser/media/media_device_id_salt.h"
 
 #include "base/base64.h"
 #include "base/rand_util.h"
 #include "chrome/browser/profiles/profile_io_data.h"
 #include "chrome/common/pref_names.h"
 #include "components/prefs/pref_service.h"
 #include "content/public/browser/browser_thread.h"
-#include "content/public/browser/resource_context.h"
 
 using content::BrowserThread;
 
-MediaDeviceIDSalt::MediaDeviceIDSalt(PrefService* pref_service) {
+namespace {
+
+std::string CreateSalt() {
+  std::string salt;
+  base::Base64Encode(base::RandBytesAsString(16), &salt);
+  DCHECK(!salt.empty());
+  return salt;
+}
+
+}  // namespace
+
+MediaDeviceIDSalt::MediaDeviceIDSalt(PrefService* pref_service,
+                                     bool incognito) {
   DCHECK_CURRENTLY_ON(BrowserThread::UI);
 
+  if (incognito) {
+    incognito_salt_ = CreateSalt();
+    return;
+  }
+
   media_device_id_salt_.Init(prefs::kMediaDeviceIdSalt, pref_service);
-  if (media_device_id_salt_.GetValue().empty()) {
-    media_device_id_salt_.SetValue(
-        content::ResourceContext::CreateRandomMediaDeviceIDSalt());
-  }
+  if (media_device_id_salt_.GetValue().empty())
+    media_device_id_salt_.SetValue(CreateSalt());
+
+  media_device_id_salt_.MoveToThread(
+      BrowserThread::GetMessageLoopProxyForThread(BrowserThread::IO));
 }
 
 MediaDeviceIDSalt::~MediaDeviceIDSalt() {
 }
 
 void MediaDeviceIDSalt::ShutdownOnUIThread() {
   DCHECK_CURRENTLY_ON(BrowserThread::UI);
-  media_device_id_salt_.Destroy();
+  if (incognito_salt_.empty())
+    media_device_id_salt_.Destroy();
 }
 
 std::string MediaDeviceIDSalt::GetSalt() const {
-  DCHECK_CURRENTLY_ON(BrowserThread::UI);
+  DCHECK_CURRENTLY_ON(BrowserThread::IO);
+  if (incognito_salt_.size())
+    return incognito_salt_;
   return media_device_id_salt_.GetValue();
 }
 
 void MediaDeviceIDSalt::RegisterProfilePrefs(
     user_prefs::PrefRegistrySyncable* registry) {
   registry->RegisterStringPref(prefs::kMediaDeviceIdSalt, std::string());
 }
 
 void MediaDeviceIDSalt::Reset(PrefService* pref_service) {
-  pref_service->SetString(
-      prefs::kMediaDeviceIdSalt,
-      content::ResourceContext::CreateRandomMediaDeviceIDSalt());
+  pref_service->SetString(prefs::kMediaDeviceIdSalt,
+                          CreateSalt());
 }