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

chrome/browser/profiles/profile_io_data.cc

Index: chrome/browser/profiles/profile_io_data.cc
diff --git a/chrome/browser/profiles/profile_io_data.cc b/chrome/browser/profiles/profile_io_data.cc
index ff66f912d7aed54c85d0a58c95ec2ff1d91e956b..64c0491627d1165f3e0f1eaf3fd87f9589efa237 100644
--- a/chrome/browser/profiles/profile_io_data.cc
+++ b/chrome/browser/profiles/profile_io_data.cc
@@ -35,6 +35,7 @@
 #include "chrome/browser/extensions/extension_resource_protocols.h"
 #include "chrome/browser/extensions/extension_system.h"
 #include "chrome/browser/io_thread.h"
+#include "chrome/browser/media/media_device_id_salt.h"
 #include "chrome/browser/net/about_protocol_handler.h"
 #include "chrome/browser/net/chrome_cookie_notification_details.h"
 #include "chrome/browser/net/chrome_fraudulent_certificate_reporter.h"
@@ -315,6 +316,7 @@ void ProfileIOData::InitializeOnUIThread(Profile* profile) {
   printing_enabled_.Init(prefs::kPrintingEnabled, pref_service);
   printing_enabled_.MoveToThread(io_message_loop_proxy);
 #endif
+
   chrome_http_user_agent_settings_.reset(
       new ChromeHttpUserAgentSettings(pref_service));
 
@@ -346,6 +348,9 @@ void ProfileIOData::InitializeOnUIThread(Profile* profile) {
     signin_allowed_.MoveToThread(io_message_loop_proxy);
   }
 
+  media_device_id_salt_.reset(new MediaDeviceIDSalt(pref_service,
+                                                    is_incognito()));
+
   // The URLBlacklistManager has to be created on the UI thread to register
   // observers of |pref_service|, and it also has to clean up on
   // ShutdownOnUIThread to release these observers on the right thread.
@@ -645,6 +650,10 @@ DesktopNotificationService* ProfileIOData::GetNotificationService() const {
 }
 #endif
 
+std::string ProfileIOData::GetMediaDeviceIDSalt() const {
+  return media_device_id_salt_->GetSalt();
+}
+
 void ProfileIOData::InitializeMetricsEnabledStateOnUIThread() {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
 #if defined(OS_CHROMEOS)
@@ -741,6 +750,10 @@ bool ProfileIOData::ResourceContext::AllowContentAccess(
   return setting == CONTENT_SETTING_ALLOW;
 }
 
+std::string ProfileIOData::ResourceContext::GetMediaDeviceIDSalt() {
+  return io_data_->GetMediaDeviceIDSalt();
+}
+
 // static
 std::string ProfileIOData::GetSSLSessionCacheShard() {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
@@ -945,6 +958,7 @@ void ProfileIOData::ShutdownOnUIThread() {
   printing_enabled_.Destroy();
   sync_disabled_.Destroy();
   signin_allowed_.Destroy();
+  media_device_id_salt_.reset(NULL);

[Jói, 2013/11/04 16:53:29]

I'm not sure this is correct (destroying it on the UI thread). I would suggest
moving ownership of MediaDeviceIDSalt to the ResourceContext object since that's
where it's used from. You could just add an is_incognito parameter to the
constructor of ResourceContext.

[perkj_chrome, 2013/11/04 19:05:38]

This is as the same as the other objects and ensures that the objects are
created and destroyed on the UI thread if I understand this correct.
 If I move the ownership I get problem that I need the  the PrefService. I can
of course add  InitializeOnUIThread(Profile* profile) on the resource context as
well but MediaDeviceIdSalt::media_device_id_salt_ (StringPrefMember) must be
destroyed on the UI thread... So in that case I need to add a 
ShutdownOnUIThread() as well on the resource context... All in all it seems
better to me to keep this? Wdyt?  

[Jói, 2013/11/04 19:24:15]

I see now from the ProfileIOData documentation that Profile will make sure to
destroy ProfileIOData on the IO thread. So either approach is fine.

[willchan no longer on Chromium, 2013/11/04 19:33:00]

Sorry, I missed this. Just to doublecheck, what thread *should* this
MediaDeviceIDSalt be used on? IO thread? If so, it should *not* be destroyed
here. This function is for objects that need 2-phase shutdown (initiate shutdown
on UI thread, and then it gets deleted on the IO thread). You're actually doing
a delete on the UI thread. If this object is used on the IO thread, then this is
wrong and will lead to a use after free.

   session_startup_pref_.Destroy();
 #if defined(ENABLE_CONFIGURATION_POLICY)
   if (url_blacklist_manager_)