Move enable extensions define to a build flag.

chrome/browser/task_manager/providers/web_contents/extension_tag.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/task_manager/providers/web_contents/extension_tag.h"
 
 #include "content/public/browser/web_contents.h"
+#include "extensions/features/features.h"
 
-#if defined(ENABLE_EXTENSIONS)
+#if BUILDFLAG(ENABLE_EXTENSIONS)
 #include "extensions/browser/process_manager.h"
 #endif
 
 namespace task_manager {
 
 ExtensionTask* ExtensionTag::CreateTask() const {
   // Upon being asked to create a task, it means that the site instance is ready
   // and connected, and the render frames have been initialized.
   // It's OK if the following returns nullptr, ExtensionTask will then get the
   // title from the WebContents.
   const extensions::Extension* extension =
       extensions::ProcessManager::Get(web_contents()->GetBrowserContext())->
           GetExtensionForWebContents(web_contents());
 
   return new ExtensionTask(web_contents(), extension, view_type_);
 }
 
 ExtensionTag::ExtensionTag(content::WebContents* web_contents,
                            const extensions::ViewType view_type)
     : WebContentsTag(web_contents),
       view_type_(view_type) {
 }
 
 ExtensionTag::~ExtensionTag() {
 }
 
 }  // namespace task_manager