chrome: fix gn check errors for utility target

Checked on Linux with the following command lines:

$ gn gen out-gn/Release --args='is_debug=false is_component_build=false
symbol_level=1'
$ gn check out-gn/Release //chrome/utility/*

BUG=367595,376000
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Review URL: https://codereview.chromium.org/1534763003

Cr-Commit-Position: refs/heads/master@{#365923}
diff --git a/.gn b/.gn
index 4b0b203..727405fb 100644
--- a/.gn
+++ b/.gn
@@ -27,6 +27,7 @@
   "//chrome/common/*",
   "//chrome/installer/*",
   "//chrome/third_party/mozilla_security_manager/*",
+  "//chrome/utility/*",
   "//chromecast/*",
   "//chrome_elf/*",
   "//cloud_print/*",