Add a policy to always show the Cast toolbar icon

chrome/browser/ui/toolbar/media_router_action_controller.h

Index: chrome/browser/ui/toolbar/media_router_action_controller.h
diff --git a/chrome/browser/ui/toolbar/media_router_action_controller.h b/chrome/browser/ui/toolbar/media_router_action_controller.h
index 346d8c5375338f4d89728c8afaacb98ad286ee59..98f6e991d1e8208f651eba7281af5c1fc93fbeea 100644
--- a/chrome/browser/ui/toolbar/media_router_action_controller.h
+++ b/chrome/browser/ui/toolbar/media_router_action_controller.h
@@ -12,6 +12,7 @@
 #include "chrome/browser/media/router/media_routes_observer.h"
 #include "chrome/browser/profiles/profile.h"
 #include "components/prefs/pref_change_registrar.h"
+#include "components/user_prefs/user_prefs.h"
 
 using extensions::ComponentMigrationHelper;
 
@@ -31,6 +32,9 @@ class MediaRouterActionController : public media_router::IssuesObserver,
       ComponentMigrationHelper* component_migration_helper);
   ~MediaRouterActionController() override;
 
+  // Whether the media router action is shown by an administrator policy.
+  static bool IsActionShownByPolicy(Profile* profile);
+
   // media_router::IssuesObserver:
   void OnIssue(const media_router::Issue& issue) override;
   void OnIssuesCleared() override;
@@ -77,6 +81,9 @@ class MediaRouterActionController : public media_router::IssuesObserver,
   bool has_issue_ = false;
   bool has_local_display_route_ = false;
 
+  // Whether the media router action is shown by an administrator policy.
+  bool shown_by_policy_;
+
   // The number of dialogs that are currently open.
   size_t dialog_count_ = 0;