Convert enable_plugins to a buildflag header.

content/browser/plugin_service_impl.h

 // 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.
 
 // This class responds to requests from renderers for the list of plugins, and
 // also a proxy object for plugin instances.
 
 #ifndef CONTENT_BROWSER_PLUGIN_SERVICE_IMPL_H_
 #define CONTENT_BROWSER_PLUGIN_SERVICE_IMPL_H_
 
-#if !defined(ENABLE_PLUGINS)
+#include "ppapi/features/features.h"
+
+#if !BUILDFLAG(ENABLE_PLUGINS)
 #error "Plugins should be enabled"
 #endif
 
 #include <map>
 #include <memory>
 #include <set>
 #include <vector>
 
 #include "base/compiler_specific.h"
 #include "base/macros.h"
@@ skipping 136 matching lines @@
 
   // Used to detect if a given plugin is crashing over and over.
   std::map<base::FilePath, std::vector<base::Time> > crash_times_;
 
   DISALLOW_COPY_AND_ASSIGN(PluginServiceImpl);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_PLUGIN_SERVICE_IMPL_H_