Add lots of testonly annotations to the GN build.

cc/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.
 
 component("cc") {
   sources = [
     "animation/animation.cc",
     "animation/animation.h",
     "animation/animation_curve.cc",
     "animation/animation_curve.h",
@@ skipping 477 matching lines @@
 
   defines = [ "CC_IMPLEMENTATION=1" ]
 
   if (!is_debug && is_win) {
     configs -= [ "//build/config/compiler:optimize" ]
     configs += [ "//build/config/compiler:optimize_max" ]
   }
 }
 
 source_set("test_support") {
+  testonly = true
   sources = [
     "test/animation_test_common.cc",
     "test/animation_test_common.h",
     "test/begin_frame_args_test.cc",
     "test/begin_frame_args_test.h",
     "test/fake_content_layer.cc",
     "test/fake_content_layer.h",
     "test/fake_content_layer_client.cc",
     "test/fake_content_layer_client.h",
     "test/fake_content_layer_impl.cc",
@@ skipping 298 matching lines @@
     "//gpu/command_buffer/common:gles2_utils",
     "//media",
     "//skia",
     "//testing/gmock",
     "//testing/gtest",
     "//testing/perf",
     "//ui/gfx",
     "//ui/gfx/geometry",
   ]
 }