Add a policy to always show the Cast toolbar icon

chrome/browser/ui/toolbar/media_router_contextual_menu.h

Index: chrome/browser/ui/toolbar/media_router_contextual_menu.h
diff --git a/chrome/browser/ui/toolbar/media_router_contextual_menu.h b/chrome/browser/ui/toolbar/media_router_contextual_menu.h
index 32bd1cac45ab204017e035887707173d9bc0896b..490814bd262ee98f339e47c7c493a89222965742 100644
--- a/chrome/browser/ui/toolbar/media_router_contextual_menu.h
+++ b/chrome/browser/ui/toolbar/media_router_contextual_menu.h
@@ -19,6 +19,9 @@ class ComponentMigrationHelper;
 class MediaRouterContextualMenu : public ui::SimpleMenuModel::Delegate {
  public:
   explicit MediaRouterContextualMenu(Browser* browser);
+
+  // Constructor for injecting values in tests.
+  MediaRouterContextualMenu(Browser* browser, bool shown_by_policy);
   ~MediaRouterContextualMenu() override;
 
   ui::MenuModel* menu_model() { return &menu_model_; }
@@ -28,6 +31,8 @@ class MediaRouterContextualMenu : public ui::SimpleMenuModel::Delegate {
                            ToggleCloudServicesItem);
   FRIEND_TEST_ALL_PREFIXES(MediaRouterContextualMenuUnitTest,
                            ToggleAlwaysShowIconItem);
+  FRIEND_TEST_ALL_PREFIXES(MediaRouterContextualMenuUnitTest,
+                           ActionShownByPolicy);
 
   // Gets or sets the "Always show icon" option.
   bool GetAlwaysShowActionPref() const;