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 a39495ef32ebc45c8380be429356c7f907e733fb..c6e6f12ab08457a643608f2ab4019e6a651725e5 100644
--- a/chrome/common/pref_names.cc
+++ b/chrome/common/pref_names.cc
@@ -2236,7 +2236,9 @@ 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.