Add gyp build for sample-extension.

runtime/dart-runtime.gyp

 # Copyright (c) 2011, 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.
 
 {
   'includes': [
     'vm/vm.gypi',
     'bin/bin.gypi',
     'third_party/double-conversion/src/double-conversion.gypi',
     'third_party/jscre/jscre.gypi',
     'tools/gyp/runtime-configurations.gypi',
     '../tools/gyp/source_filter.gypi',
+    '../samples/sample_extension/sample_extension.gypi',
   ],
   'targets': [
     {
       'target_name': 'libdart',
       'type': 'static_library',
       'dependencies': [
         'libdart_lib',
         'libdart_vm',
         'libjscre',
         'libdouble_conversion',
@@ skipping 37 matching lines @@
         'DART_SHARED_LIB',
       ],
       'direct_dependent_settings': {
         'include_dirs': [
           'include',
         ],
       },
     },
   ],
 }