Add lots of testonly annotations to the GN build.

ui/compositor/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")
 
 component("compositor") {
   sources = [
     "closure_animation_observer.cc",
     "closure_animation_observer.h",
@@ skipping 60 matching lines @@
     # IDR_BITMAP_BRUSH_IMAGE.
     deps += [
       "//ui/resources",
       "//third_party/angle:libEGL",
       "//third_party/angle:libGLESv2",
     ]
   }
 }
 
 source_set("test_support") {
+  testonly = true
   sources = [
     "test/context_factories_for_test.cc",
     "test/context_factories_for_test.h",
     "test/draw_waiter_for_test.cc",
     "test/draw_waiter_for_test.h",
     "test/in_process_context_factory.cc",
     "test/in_process_context_factory.h",
     "test/layer_animator_test_controller.cc",
     "test/layer_animator_test_controller.h",
     "test/test_compositor_host.h",
@@ skipping 64 matching lines @@
 #    "//ui/gfx",
 #    "//ui/gfx/geometry",
 #    "//ui/gl",
 #    "//ui/resources",
 #  ]
 #
 #  if (is_linux) {
 #    deps += [ "//third_party/mesa:osmesa" ]
 #  }
 #}