Add remaining trivial targets for the Linux GN build

gpu/tools/tools.gyp

 # Copyright (c) 2012 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.
 
 {
   'variables': {
     'chromium_code': 1,
   },
   'targets': [
   ],
   'conditions': [
     ['OS == "linux" and target_arch != "arm" and use_x11==1', {
       'targets': [
         {
+          # GN: //gpu:compositor_model_bench
           'target_name': 'compositor_model_bench',
           'type': 'executable',
           'dependencies': [
             '../../base/base.gyp:base',
             '../../build/linux/system.gyp:x11',
             '../../ui/gl/gl.gyp:gl',
           ],
           'libraries': [
             '-lGL',
             '-ldl',
           ],
           'sources': [
             'compositor_model_bench/compositor_model_bench.cc',
             'compositor_model_bench/forward_render_model.cc',
             'compositor_model_bench/render_model_utils.cc',
             'compositor_model_bench/render_models.cc',
             'compositor_model_bench/render_tree.cc',
             'compositor_model_bench/shaders.cc',
           ],
         },
       ],
     }],
   ],
 }