Show the Cast toolbar icon ephemerally when Cast is in use

chrome/common/pref_names.cc

Index: chrome/common/pref_names.cc
diff --git a/chrome/common/pref_names.cc b/chrome/common/pref_names.cc
index c5e2281e46302123a519a601b8829dcd848ac14b..6eeb338155415001d6aa5c6beb459068ca679891 100644
--- a/chrome/common/pref_names.cc
+++ b/chrome/common/pref_names.cc
@@ -2251,7 +2251,9 @@ const char kMediaRouterEnableCloudServices[] =
 // user.
 const char kMediaRouterFirstRunFlowAcknowledged[] =
     "media_router.firstrunflow.acknowledged";
-#endif
+const char kMediaRouterAlwaysShowActionIcon[] =
+    "media_router.action.always_show";
+#endif  // defined(ENABLE_MEDIA_ROUTER)
 
 // The base64-encoded representation of the public key to use to validate origin
 // trial token signatures.