Add lots of testonly annotations to the GN build.

sync/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")
 
 component("sync") {
   deps = [
     ":sync_core",
     "//sync/protocol",
@@ skipping 691 matching lines @@
     "//testing/gtest",
     "//third_party/protobuf:protobuf_lite",
     "//sync",
   ]
 
   configs += [ "//build/config/compiler:wexit_time_destructors" ]
 }
 
 # GYP version: sync/sync_tests.gypi:test_support_sync_testserver
 static_library("test_support_sync_testserver") {
+  testonly = true
   sources = [
     "test/local_sync_test_server.cc",
     "test/local_sync_test_server.h",
   ]
 
   configs += [ "//build/config/compiler:wexit_time_destructors" ]
 
   deps = [
     "//base",
     "//net:test_support",
     ":sync",
 
     # The sync test server uses Python modules generated by the sync protos.
     #  '../third_party/protobuf/protobuf.gyp:py_proto',  # TODO(GYP)
   ]
 
   forward_dependent_configs_from = [ "//base", "//net:test_support" ]
 }
 
 # GYP version: sync/sync_tests.gypi:test_support_accounts_client
 static_library("test_support_accounts_client") {
+  testonly = true
   sources = [
     "test/accounts_client/test_accounts_client.cc",
     "test/accounts_client/test_accounts_client.h",
     "test/accounts_client/url_request_context_getter.cc",
     "test/accounts_client/url_request_context_getter.h",
   ]
   deps = [
     "//base",
     "//net",
   ]
 }
 
 # GYP version: sync/sync_tests.gypi:sync_endtoend_tests
 test("sync_endtoend_tests") {
   sources = [
     "test/accounts_client/test_accounts_client_unittest.cc",
   ]
   deps = [
     "//base/test:run_all_unittests",
     "//testing/gmock",
     "//testing/gtest",
     "//url",
     ":test_support_accounts_client",
   ]
 }
 
 if (!is_ios) {
   # GYP version: sync/sync_tests.gypi:run_sync_testserver
   executable("run_sync_testserver") {
+    testonly = true
     sources = [ "tools/testserver/run_sync_testserver.cc" ]
 
     deps = [
       "//base",
       "//base/test:test_support",
       "//net:test_support",
       "//testing/gtest",
       ":test_support_sync_testserver",
     ]
   }
 }
 
 #TODO(GYP): Need to port sync_android.gypi and Android test targets.