Add samples gyp target to Dart project, that builds samples/sample_extension.

samples/sample_extension/sample_extension.gypi

-# Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
-# for details. 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': 'sample_extension',
-      'type': 'shared_library',
-      'dependencies': [
-        'dart',
-      ],
-      'include_dirs': [
-        '../../runtime/include',
-      ],
-      'sources': [
-        'sample_extension.cc',
-        'sample_extension_dllmain_win.cc',
-      ],
-      'defines': [
-        'DART_SHARED_LIB',
-      ],
-      'conditions': [
-        ['OS=="win"', {
-          'msvs_settings': {
-            'VCLinkerTool': {
-              'AdditionalDependencies': [ 'dart.lib' ],
-              'AdditionalLibraryDirectories': [ '<(PRODUCT_DIR)' ],
-            },
-          },
-        }],
-        ['OS=="mac"', {
-          'xcode_settings': {
-            'OTHER_LDFLAGS': [ '-undefined', 'dynamic_lookup' ],
-          },
-        }],
-      ],
-    },
-  ],
-}