Add lots of testonly annotations to the GN build.

ui/gfx/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/ui.gni")
 
 if (is_android) {
   import("//build/config/android/config.gni")
   import("//build/config/android/rules.gni")
 }
@@ skipping 346 matching lines @@
   if (use_pango && use_ozone) {
     sources -= [
       "platform_font_ozone.cc",
     ]
   }
 }
 
 # Looking for gfx_geometry? It's //ui/gfx/geometry:geometry
 
 source_set("test_support") {
+  testonly = true
   sources = [
     "test/fontconfig_util_linux.cc",
     "test/fontconfig_util_linux.h",
     "test/gfx_util.cc",
     "test/gfx_util.h",
     "test/ui_cocoa_test_helper.h",
     "test/ui_cocoa_test_helper.mm",
   ]
 
   deps = [
@@ skipping 62 matching lines @@
 if (is_android) {
   generate_jni("gfx_jni_headers") {
     sources = [
       "../android/java/src/org/chromium/ui/gfx/BitmapHelper.java",
       "../android/java/src/org/chromium/ui/gfx/DeviceDisplayInfo.java",
       "../android/java/src/org/chromium/ui/gfx/ViewConfigurationHelper.java",
     ]
     jni_package = "gfx"
   }
 }