Add lots of testonly annotations to the GN build.

ash/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/features.gni")
 import("//build/config/ui.gni")
 
 gypi_values = exec_script(
     "//build/gypi_to_gn.py",
     [ rebase_path("ash.gyp") ],
@@ skipping 147 matching lines @@
     "//ui/web_dialogs",
     "//url",
   ]
 
   forward_dependent_configs_from = [
     ":ash",
   ]
 }
 
 static_library("test_support") {
+  testonly = true
   sources = gypi_values.ash_test_support_sources
 
   deps = [
     ":ash",
     "//ash/resources",
     "//content/test:test_support",
     "//skia",
     "//testing/gtest",
     "//ui/accessibility",
     "//ui/app_list",
@@ skipping 13 matching lines @@
       "//ipc",
       #'../ui/metro_viewer/metro_viewer.gyp:metro_viewer_messages',  TODO(GYP)
       #'../win8/win8.gyp:metro_viewer',  TODO(GYP)
       #'../win8/win8.gyp:test_support_win8',  TODO(GYP)
       #'../win8/win8_tests.gyp:test_registrar',  TODO(GYP)
     ]
   }
 }
 
 static_library("ash_shell_lib") {
+  testonly = true
   sources = gypi_values.ash_shell_lib_sources
 
   deps = [
     ":ash",
     ":ash_with_content",
     ":test_support",
     "//ash/resources",
     "//ash/strings",
     "//base",
     "//base:i18n",
@@ skipping 120 matching lines @@
   # ldflags = "-rdynamic"
 
   if (use_ozone) {
     sources -= [
       "sticky_keys/sticky_keys_unittest.cc",  # crbug.com/354035
     ]
   }
 }
 
 executable("ash_shell") {
+  testonly = true
   sources = [
     "shell/shell_main.cc",
   ]
 
   deps = [
     ":ash_shell_lib",
     "//components/user_manager",
   ]
 
   if (is_win) {
@@ skipping 25 matching lines @@
     "//testing/gtest",
     "//ui/aaccessibility",
   ]
 
   if (is_chromeos) {
     deps += [ "//ui/display" ]
   }
 }
 
 }  # if false