Convert enable_plugins to a buildflag header.

components/renderer_context_menu/BUILD.gn

 # 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.
 
 import("//build/config/ui.gni")
 
 static_library("renderer_context_menu") {
   sources = [
     "context_menu_content_type.cc",
     "context_menu_content_type.h",
     "context_menu_delegate.cc",
     "context_menu_delegate.h",
     "render_view_context_menu_base.cc",
     "render_view_context_menu_base.h",
     "render_view_context_menu_observer.cc",
     "render_view_context_menu_observer.h",
     "render_view_context_menu_proxy.h",
   ]
 
   deps = [
     "//base",
     "//components/search_engines",
     "//content/public/browser",
     "//content/public/common",
+    "//ppapi/features",
     "//printing/features",
     "//third_party/WebKit/public:blink_headers",
     "//ui/base",
   ]
 
   if (toolkit_views) {
     sources += [
       "views/toolkit_delegate_views.cc",
       "views/toolkit_delegate_views.h",
     ]
     deps += [ "//ui/views" ]
   }
 }