Mark gtest and gmock as testonly in GN.

ui/gl/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 298 matching lines @@
         rebase_path("//gpu", root_build_dir),
     rebase_path(gl_binding_output_dir, root_build_dir),
   ]
 }
 
 config("gl_unittest_utils_config") {
   include_dirs = [ gl_binding_output_dir ]
 }
 
 source_set("gl_unittest_utils") {
+  testonly = true
   sources = [
     "gl_mock.h",
     "gl_mock.cc",
     "$gl_binding_output_dir/gl_bindings_autogen_mock.cc",
     "$gl_binding_output_dir/gl_bindings_autogen_mock.h",
     "$gl_binding_output_dir/gl_mock_autogen_gl.h",
   ]
 
   configs += [ "//third_party/khronos:khronos_headers" ]
   direct_dependent_configs = [ ":gl_unittest_utils_config" ]
@@ skipping 13 matching lines @@
   generate_jni("gl_jni_headers") {
     deps = [ ":surface_jni_headers" ]
     forward_dependent_configs_from = [ ":surface_jni_headers" ]
     sources = [
       "../android/java/src/org/chromium/ui/gl/SurfaceTextureListener.java",
       "../android/java/src/org/chromium/ui/gl/SurfaceTexturePlatformWrapper.java",
     ]
     jni_package = "ui/gl"
   }
 }