Expose the MacViewsWebUIDialogs feature flag to chrome://flags

chrome/browser/ui/browser_dialogs_mac.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/ui/browser_dialogs.h"
 
-#include "base/command_line.h"
 #include "base/feature_list.h"
-#include "chrome/common/chrome_switches.h"
+
+namespace chrome {
+
+const base::Feature kMacViewsNativeDialogs {
+  "MacViewsNativeDialogs", base::FEATURE_DISABLED_BY_DEFAULT
+};
 
 const base::Feature kMacViewsWebUIDialogs {
   "MacViewsWebUIDialogs", base::FEATURE_DISABLED_BY_DEFAULT
 };
 
-namespace chrome {
-
 bool ToolkitViewsDialogsEnabled() {
-  return base::CommandLine::ForCurrentProcess()->HasSwitch(
-      switches::kEnableMacViewsDialogs);
+  return base::FeatureList::IsEnabled(kMacViewsNativeDialogs);
 }
 
 bool ToolkitViewsWebUIDialogsEnabled() {
   return base::FeatureList::IsEnabled(kMacViewsWebUIDialogs);
 }
 
 }  // namespace chrome