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

chrome/browser/prefs/browser_prefs.cc

Index: chrome/browser/prefs/browser_prefs.cc
diff --git a/chrome/browser/prefs/browser_prefs.cc b/chrome/browser/prefs/browser_prefs.cc
index 58eb9c2215c77525d611403ff3e4eb8a241b101f..b1d962ee42e7d14c324507c99d3e95e3a5e2a20f 100644
--- a/chrome/browser/prefs/browser_prefs.cc
+++ b/chrome/browser/prefs/browser_prefs.cc
@@ -37,6 +37,7 @@
 #include "chrome/browser/intranet_redirect_detector.h"
 #include "chrome/browser/io_thread.h"
 #include "chrome/browser/media/media_capture_devices_dispatcher.h"
+#include "chrome/browser/media/media_device_id_salt.h"
 #include "chrome/browser/media/media_stream_devices_controller.h"
 #include "chrome/browser/metrics/metrics_log.h"
 #include "chrome/browser/metrics/metrics_service.h"
@@ -346,6 +347,7 @@ void RegisterProfilePrefs(user_prefs::PrefRegistrySyncable* registry) {
   InstantUI::RegisterProfilePrefs(registry);
   MediaCaptureDevicesDispatcher::RegisterProfilePrefs(registry);
   MediaStreamDevicesController::RegisterProfilePrefs(registry);
+  MediaDeviceIDSalt::RegisterProfilePrefs(registry);
   NetPrefObserver::RegisterProfilePrefs(registry);
   NetworkTimeService::RegisterProfilePrefs(registry);
   NewTabUI::RegisterProfilePrefs(registry);