Show the Cast toolbar icon ephemerally when Cast is in use

chrome/browser/extensions/component_migration_helper.cc

Index: chrome/browser/extensions/component_migration_helper.cc
diff --git a/chrome/browser/extensions/component_migration_helper.cc b/chrome/browser/extensions/component_migration_helper.cc
index 3a3c1a3ef3190cc7b6d6057c893c00aed843f263..95432c2ec6fbb6501a3f0e9a499a9e1dd45bf086 100644
--- a/chrome/browser/extensions/component_migration_helper.cc
+++ b/chrome/browser/extensions/component_migration_helper.cc
@@ -9,6 +9,7 @@
 #include "chrome/browser/extensions/extension_service.h"
 #include "chrome/browser/extensions/extension_system_impl.h"
 #include "chrome/browser/profiles/profile.h"
+#include "chrome/browser/ui/toolbar/component_toolbar_actions_factory.h"
 #include "chrome/common/pref_names.h"
 #include "components/prefs/pref_registry_simple.h"
 #include "components/prefs/pref_service.h"
@@ -134,6 +135,12 @@ void ComponentMigrationHelper::OnExtensionReady(
     UnloadExtension(extension_id);
     SetComponentActionPref(component_action_id, true);
 
+    if (component_action_id ==
+        ComponentToolbarActionsFactory::kMediaRouterActionId) {
+      pref_service_->SetBoolean(prefs::kMediaRouterAlwaysShowActionIcon,

[Devlin, 2016/08/02 20:18:51]

Thinking about this, this probably warrants a comment.  Something like:
// We treat installation of the cast extension as a signal to permanently
// show the icon in the toolbar.

[takumif, 2016/08/03 22:03:50]

Done.

+                                true);
+    }
+
     if (!delegate_->HasComponentAction(component_action_id))
       delegate_->AddComponentAction(component_action_id);
   }