Allow dynamic change to WebRTC's multiple_routes_enabled preference.

chrome/browser/ui/prefs/prefs_tab_helper.cc

Index: chrome/browser/ui/prefs/prefs_tab_helper.cc
diff --git a/chrome/browser/ui/prefs/prefs_tab_helper.cc b/chrome/browser/ui/prefs/prefs_tab_helper.cc
index b1c23df4a8bd482a36eb1ed74f70b1e4c567ab19..44f5caefc6ae3cdb6b6fe12b4bd17741ffe43104 100644
--- a/chrome/browser/ui/prefs/prefs_tab_helper.cc
+++ b/chrome/browser/ui/prefs/prefs_tab_helper.cc
@@ -352,6 +352,11 @@ class PrefWatcher : public KeyedService {
     pref_change_registrar_.Add(prefs::kEnableDoNotTrack, renderer_callback);
     pref_change_registrar_.Add(prefs::kEnableReferrers, renderer_callback);
 
+#if defined(ENABLE_WEBRTC)
+    pref_change_registrar_.Add(prefs::kWebRTCMultipleRoutesEnabled,
+                               renderer_callback);
+#endif
+
 #if !defined(OS_MACOSX)
     pref_change_registrar_.Add(prefs::kFullscreenAllowed, renderer_callback);
 #endif