[Media Router] Adds a contextual menu item to remove the MR component action.

chrome/browser/ui/toolbar/toolbar_actions_model.h

Index: chrome/browser/ui/toolbar/toolbar_actions_model.h
diff --git a/chrome/browser/ui/toolbar/toolbar_actions_model.h b/chrome/browser/ui/toolbar/toolbar_actions_model.h
index c2ba29896b4312af296ac06df334efd91de26029..e288edc3256e0e89ad603d342edac32719bfc66c 100644
--- a/chrome/browser/ui/toolbar/toolbar_actions_model.h
+++ b/chrome/browser/ui/toolbar/toolbar_actions_model.h
@@ -178,6 +178,12 @@ class ToolbarActionsModel
   void RemoveComponentAction(const std::string& action_id) override;
   bool HasComponentAction(const std::string& action_id) const override;
 
+  // Returns this toolbar's component migration helper.  The helper is owned by
+  // |this|.
+  extensions::ComponentMigrationHelper* component_migration_helper() {
+    return component_migration_helper_.get();
+  }
+
   void OnActionToolbarPrefChange();
 
   // Highlights the actions specified by |action_ids|. This will cause