Improve content test GN build

ppapi/ppapi_tests.gypi

 # 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.
 
 {
   'targets': [
     {
       'target_name': 'ppapi_tests',
       'type': 'loadable_module',
       'include_dirs': [
@@ skipping 65 matching lines @@
 #            'tests/test_c_includes.c',
 #            'tests/test_cc_includes.cc',
 #          ],
 #          'action': [
 #            '<!@(python generate_ppapi_include_tests.py)',
 #          ],
 #        },
 #      ],
     },
     {
+      # GN version: //ppapi:ppapi_unittest_shared
       'target_name': 'ppapi_unittest_shared',
       'type': 'static_library',
       'dependencies': [
         'ppapi_proxy',
         'ppapi_shared',
         '../base/base.gyp:test_support_base',
         '../ipc/ipc.gyp:ipc',
         '../ipc/ipc.gyp:test_support_ipc',
         '../testing/gmock.gyp:gmock',
         '../testing/gtest.gyp:gtest',
       ],
       'sources': [
+        # Note: sources list duplicated in GN build.
         'proxy/ppapi_proxy_test.cc',
         'proxy/ppapi_proxy_test.h',
         'proxy/resource_message_test_sink.cc',
         'proxy/resource_message_test_sink.h',
         'shared_impl/test_globals.cc',
         'shared_impl/test_globals.h',
         'shared_impl/unittest_utils.cc',
         'shared_impl/unittest_utils.h',
       ],
     },
@@ skipping 473 matching lines @@
         'lib/gl/include',
       ],
       'sources': [
         'examples/compositor/compositor.cc',
         'examples/compositor/spinning_cube.cc',
         'examples/compositor/spinning_cube.h',
       ],
     },
   ],
 }