Mark gtest and gmock as testonly in GN.

jingle/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")
 
 if (enable_webrtc || !is_android) {
   jingle_includes = exec_script("//build/gypi_to_gn.py",
                                 [ rebase_path("jingle.gypi") ],
                                 "scope",
@@ skipping 72 matching lines @@
       "//third_party/expat",
       "//url",
       ":jingle_glue",
       "//third_party/libjingle",
     ]
     forward_dependent_configs_from = [ "//third_party/libjingle" ]
   }
 
   # GYP version: jingle/jingle.gyp:notifier_test_util
   static_library("notifier_test_util") {
+    testonly = true
     sources = [
       "notifier/base/fake_base_task.cc",
       "notifier/base/fake_base_task.h",
       "notifier/listener/fake_push_client.cc",
       "notifier/listener/fake_push_client.h",
       "notifier/listener/fake_push_client_observer.cc",
       "notifier/listener/fake_push_client_observer.h",
     ]
     deps = [
       ":notifier",
@@ skipping 77 matching lines @@
       "notifier/base/notifier_options.h",
     ]
     deps = [
       "//base",
       "//net"
     ]
   }
 
   source_set("notifier_test_util") { }
 }