Move enable extensions define to a build flag.

chrome/browser/ui/blocked_content/app_modal_dialog_helper.cc

 // Copyright 2014 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/blocked_content/app_modal_dialog_helper.h"
 
 #include "chrome/browser/ui/browser.h"
 #include "chrome/browser/ui/browser_finder.h"
 #include "chrome/browser/ui/browser_list.h"
 #include "chrome/browser/ui/tabs/tab_strip_model.h"
 #include "content/public/browser/web_contents.h"
 #include "content/public/browser/web_contents_delegate.h"
+#include "extensions/features/features.h"
 
-#if defined(ENABLE_EXTENSIONS)
+#if BUILDFLAG(ENABLE_EXTENSIONS)
 #include "components/guest_view/browser/guest_view_base.h"
 #endif
 
 AppModalDialogHelper::AppModalDialogHelper(content::WebContents* dialog_host)
     : popup_(nullptr) {
   content::WebContents* actual_host = dialog_host;
-#if defined(ENABLE_EXTENSIONS)
+#if BUILDFLAG(ENABLE_EXTENSIONS)
   // If the dialog was triggered via an PDF, get the actual web contents that
   // embedds the PDF.
   guest_view::GuestViewBase* guest =
       guest_view::GuestViewBase::FromWebContents(dialog_host);
   if (guest)
     actual_host = guest->embedder_web_contents();
 #endif
 
   // If the WebContents that triggered this dialog is not currently focused, we
   // want to store a potential popup here to restore it after the dialog was
@@ skipping 13 matching lines @@
 }
 
 AppModalDialogHelper::~AppModalDialogHelper() {
   if (popup_)
     popup_->GetDelegate()->ActivateContents(popup_);
 }
 
 void AppModalDialogHelper::WebContentsDestroyed() {
   popup_ = nullptr;
 }