MacViews: Consolidate flags. Just use --secondary-ui-md to enable MacViews.

chrome/browser/ui/cocoa/extensions/extension_install_dialog_controller.mm

 // Copyright (c) 2012 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.
 
 #import "chrome/browser/ui/cocoa/extensions/extension_install_dialog_controller.h"
 
 #include <utility>
 
 #include "base/bind.h"
 #include "base/callback_helpers.h"
 #include "base/logging.h"
 #include "base/memory/ref_counted.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "chrome/browser/extensions/api/experience_sampling_private/experience_sampling.h"
 #include "chrome/browser/extensions/extension_install_prompt_show_params.h"
 #include "chrome/browser/ui/browser.h"
-#include "chrome/browser/ui/browser_dialogs.h"
 #include "chrome/browser/ui/browser_finder.h"
 #import "chrome/browser/ui/cocoa/constrained_window/constrained_window_custom_sheet.h"
 #include "chrome/browser/ui/cocoa/constrained_window/constrained_window_custom_window.h"
 #import "chrome/browser/ui/cocoa/extensions/windowed_install_dialog_controller.h"
 #include "chrome/browser/ui/tabs/tab_strip_model.h"
 #include "content/public/browser/web_contents.h"
+#include "ui/base/material_design/material_design_controller.h"
 
 using extensions::ExperienceSamplingEvent;
 
 namespace {
 
 void ShowExtensionInstallDialogImpl(
     ExtensionInstallPromptShowParams* show_params,
     const ExtensionInstallPrompt::DoneCallback& done_callback,
     std::unique_ptr<ExtensionInstallPrompt::Prompt> prompt) {
   // These objects will delete themselves when the dialog closes.
@@ skipping 72 matching lines @@
     const char* decision_event) {
   if (sampling_event_.get())
     sampling_event_->CreateUserDecisionEvent(decision_event);
   base::ResetAndReturn(&done_callback_).Run(result);
   constrained_window_->CloseWebContentsModalDialog();
 }
 
 // static
 ExtensionInstallPrompt::ShowDialogCallback
 ExtensionInstallPrompt::GetDefaultShowDialogCallback() {
-  if (chrome::ToolkitViewsWebUIDialogsEnabled())
+  if (ui::MaterialDesignController::IsSecondaryUiMaterial())
     return ExtensionInstallPrompt::GetViewsShowDialogCallback();
   return base::Bind(&ShowExtensionInstallDialogImpl);
 }