Add lots of testonly annotations to the GN build.

content/shell/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")
 import("//tools/grit/grit_rule.gni")
 import("//tools/grit/repack.gni")
 if (is_android) {
   import("//build/config/android/config.gni")
 }
 
 declare_args() {
   content_shell_product_name = "Content Shell"
 
   # The "19" is so that sites that sniff for version think that this is
   # something reasonably current; the "77.34.5" is a hint that this isn't a
   # standard Chrome.
   content_shell_version = "19.77.34.5"
 }
 
 static_library("content_shell_lib") {
+  testonly = true
   sources = [
     "android/shell_jni_registrar.cc",
     "android/shell_jni_registrar.h",
     "android/shell_manager.cc",
     "android/shell_manager.h",
     "app/paths_mac.h",
     "app/paths_mac.mm",
     "app/shell_breakpad_client.cc",
     "app/shell_breakpad_client.h",
     "app/shell_main_delegate.cc",
@@ skipping 388 matching lines @@
   if (is_android) {
     output = "$root_out_dir/content_shell/assets/content_shell.pak"
   } else {
     sources += [ "$root_gen_dir/webkit/devtools_resources.pak" ]
     deps += [ "//content/browser/devtools:resources" ]
     output = "$root_out_dir/content_shell.pak"
   }
 }
 
 executable("content_shell") {
+  testonly = true
   # TODO(GYP) mac resource bundle stuff for this target.
   # TODO(GYP) Windows content shell settings:
   #  - Manifest.
   #  - RC file.
   #  - 'LinkIncremental': '<(msvs_large_module_debug_link_mode)',
   sources = [
     "../app/startup_helper_win.cc",
     "app/shell_main.cc",
   ]
 
@@ skipping 17 matching lines @@
   }
 
   if (!is_android || !is_android_webview_build) {
     # Some tests rely on this tool. It might be nicer if these tests relied on
     # image diff rather than having content shell depend on it.
     datadeps = [
       "//tools/imagediff($host_toolchain)",
     ]
   }
 }