Add lots of testonly annotations to the GN build.

base/test/BUILD.gn

 # Copyright (c) 2013 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")
 
 if (is_android) {
   import("//build/config/android/rules.gni")
 }
 
 source_set("test_support") {
+  testonly = true
   sources = [
     "expectations/expectation.cc",
     "expectations/expectation.h",
     "expectations/parser.cc",
     "expectations/parser.h",
     "gtest_xml_util.cc",
     "gtest_xml_util.h",
     "histogram_tester.cc",
     "histogram_tester.h",
     "launcher/test_launcher.cc",
@@ skipping 105 matching lines @@
   if (is_android) {
     deps += [ ":base_unittests_jni_headers" ]
   }
 }
 
 config("perf_test_config") {
   defines = [ "PERF_TEST" ]
 }
 
 source_set("test_support_perf") {
+  testonly = true
   sources = [
     "run_all_perftests.cc",
   ]
   deps = [
     ":test_support",
     "//base",
     "//testing/gtest",
   ]
 
   direct_dependent_configs = [ ":perf_test_config" ]
 }
 
 source_set("run_all_unittests") {
+  testonly = true
   sources = [
     "run_all_unittests.cc",
   ]
   deps = [
     ":test_support",
   ]
 }
 
 if (is_android) {
   generate_jni("base_unittests_jni_headers") {
     sources = [
       "android/java/src/org/chromium/base/ContentUriTestUtils.java",
     ]
     jni_package = "base"
   }
 }