Convert enable_plugins to a buildflag header.

chrome/test/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/chrome_build.gni")
 import("//build/config/compiler/compiler.gni")
 import("//build/config/crypto.gni")
 import("//build/config/features.gni")
 import("//build/config/ui.gni")
 import("//chrome/common/features.gni")
@@ skipping 109 matching lines @@
     "//components/sync_sessions:test_support",
     "//components/toolbar:test_support",
     "//components/update_client:test_support",
     "//components/zoom:test_support",
     "//content/public/app:both",
     "//content/test:test_support",
     "//extensions/features",
     "//gpu/ipc/service",
     "//net",
     "//net:test_support",
+    "//ppapi/features",
     "//printing/features",
     "//skia",
     "//sql",
     "//sql:test_support",
     "//testing/gmock",
     "//testing/gtest",
     "//third_party/zlib",
     "//ui/gfx:test_support",
     "//ui/message_center:test_support",
   ]
@@ skipping 1084 matching lines @@
   configs += [ "//build/config:precompiled_headers" ]
 
   deps = [
     ":browser_tests_runner",
     ":repack_pseudo_locales",
     ":test_support",
     "//base",
     "//components/spellcheck:build_features",
     "//components/sync:test_support_model",
     "//extensions/features",
+    "//ppapi/features",
     "//printing/features",
     "//third_party/WebKit/public:features",
   ]
 
   data_deps = [
     "//testing/buildbot/filters:browser_tests_filters",
   ]
 
   data = []
 
@@ skipping 3854 matching lines @@
       "touch_hud",
       "ui",
     ]
 
     if (is_linux && !is_android) {
       deps += [ "//components/font_service:manifest" ]
       packaged_services += [ "font_service" ]
     }
   }
 }