Convert enable_plugins to a buildflag header.

content/shell/browser/layout_test/layout_test_browser_main_parts.h

 // 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.
 
 #ifndef CONTENT_SHELL_BROWSER_LAYOUT_TEST_LAYOUT_TEST_BROWSER_MAIN_PARTS_H_
 #define CONTENT_SHELL_BROWSER_LAYOUT_TEST_LAYOUT_TEST_BROWSER_MAIN_PARTS_H_
 
 #include <memory>
 
 #include "base/macros.h"
 #include "build/build_config.h"
 #include "content/shell/browser/shell_browser_main_parts.h"
+#include "ppapi/features/features.h"
 
 namespace content {
 
 class ShellPluginServiceFilter;
 
 class LayoutTestBrowserMainParts : public ShellBrowserMainParts {
  public:
   explicit LayoutTestBrowserMainParts(const MainFunctionParams& parameters);
   ~LayoutTestBrowserMainParts() override;
 
  private:
   void InitializeBrowserContexts() override;
   void InitializeMessageLoopContext() override;
 
-#if defined(ENABLE_PLUGINS)
+#if BUILDFLAG(ENABLE_PLUGINS)
   std::unique_ptr<ShellPluginServiceFilter> plugin_service_filter_;
 #endif
 
   DISALLOW_COPY_AND_ASSIGN(LayoutTestBrowserMainParts);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_SHELL_BROWSER_LAYOUT_TEST_LAYOUT_TEST_BROWSER_MAIN_PARTS_H_