Implement a salt for MediaSource IDs that can be cleared by a user.

chrome/browser/media/media_device_id_salt.cc

Index: chrome/browser/media/media_device_id_salt.cc
diff --git a/chrome/browser/media/media_device_id_salt.cc b/chrome/browser/media/media_device_id_salt.cc
new file mode 100644
index 0000000000000000000000000000000000000000..27da539cd8aefd1ce2b72ed85fad9d37506b8707
--- /dev/null
+++ b/chrome/browser/media/media_device_id_salt.cc
@@ -0,0 +1,70 @@
+// 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/prefs/pref_service.h"
+#include "base/rand_util.h"
+#include "chrome/browser/profiles/profile_io_data.h"
+#include "chrome/common/pref_names.h"
+#include "content/public/browser/browser_thread.h"
+
+using content::BrowserThread;
+
+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(BrowserThread::CurrentlyOn(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(CreateSalt());
+
+  media_device_id_salt_.MoveToThread(
+      BrowserThread::GetMessageLoopProxyForThread(BrowserThread::IO));
+}
+
+MediaDeviceIDSalt::~MediaDeviceIDSalt() {
+}
+
+void MediaDeviceIDSalt::ShutdownOnUIThread() {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+  if (incognito_salt_.empty())
+    media_device_id_salt_.Destroy();
+}
+
+std::string MediaDeviceIDSalt::GetSalt() const {
+  DCHECK(BrowserThread::CurrentlyOn(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(),
+      user_prefs::PrefRegistrySyncable::UNSYNCABLE_PREF);
+}
+
+void MediaDeviceIDSalt::Reset(PrefService* pref_service) {
+  pref_service->SetString(prefs::kMediaDeviceIdSalt,
+                          CreateSalt());
+}