chrome::ShowTaskManager: refine return type to eliminate a downcast.

chrome/browser/task_management/task_manager_tester.cc

Index: chrome/browser/task_management/task_manager_tester.cc
diff --git a/chrome/browser/task_management/task_manager_tester.cc b/chrome/browser/task_management/task_manager_tester.cc
index 627ab684d4f4c03e70799e51875375d012c7bede..55405552475b0e8e784979f892af100120782bc4 100644
--- a/chrome/browser/task_management/task_manager_tester.cc
+++ b/chrome/browser/task_management/task_manager_tester.cc
@@ -145,11 +145,7 @@ class TaskManagerTesterImpl : public TaskManagerTester {
 
   // Returns the TaskManagerTableModel for the the visible NewTaskManagerView.
   static task_management::TaskManagerTableModel* GetRealModel() {
-    // This downcast is safe, as long as the new task manager is enabled.
-    task_management::TaskManagerTableModel* result =
-        static_cast<task_management::TaskManagerTableModel*>(
-            chrome::ShowTaskManager(nullptr));
-    return result;
+    return chrome::ShowTaskManager(nullptr);
   }
 
   task_management::TaskManagerTableModel* model_;