[tab-under] Add pref to turn feature off

A followup will hook this pref with a new enterprise policy to turn the
feature off.

Bug: 823700
Change-Id: I06096460a372941ba06f3bf3e9cc63b9084f82cd
Reviewed-on: https://chromium-review.googlesource.com/970729
Reviewed-by: Avi Drissman <[email protected]>
Reviewed-by: Bernhard Bauer <[email protected]>
Commit-Queue: Charlie Harrison <[email protected]>
Cr-Commit-Position: refs/heads/master@{#544375}
diff --git a/chrome/browser/prefs/browser_prefs.cc b/chrome/browser/prefs/browser_prefs.cc
index cf45dbf..a1bb49f 100644
--- a/chrome/browser/prefs/browser_prefs.cc
+++ b/chrome/browser/prefs/browser_prefs.cc
@@ -55,6 +55,7 @@
 #include "chrome/browser/task_manager/task_manager_interface.h"
 #include "chrome/browser/tracing/chrome_tracing_delegate.h"
 #include "chrome/browser/ui/blocked_content/safe_browsing_triggered_popup_blocker.h"
+#include "chrome/browser/ui/blocked_content/tab_under_navigation_throttle.h"
 #include "chrome/browser/ui/browser_ui_prefs.h"
 #include "chrome/browser/ui/navigation_correction_tab_observer.h"
 #include "chrome/browser/ui/network_profile_bubble.h"
@@ -525,6 +526,7 @@
   SessionStartupPref::RegisterProfilePrefs(registry);
   signin::RegisterAccountConsistencyProfilePrefs(registry);
   syncer::SyncPrefs::RegisterProfilePrefs(registry);
+  TabUnderNavigationThrottle::RegisterProfilePrefs(registry);
   TemplateURLPrepopulateData::RegisterProfilePrefs(registry);
   translate::TranslatePrefs::RegisterProfilePrefs(registry);
   UINetworkQualityEstimatorService::RegisterProfilePrefs(registry);