Add native extensions to the Dart shell, on the linux platform.

runtime/bin/bin.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.
 
 {
   'variables': {
     'io_cc_file': '<(SHARED_INTERMEDIATE_DIR)/io_gen.cc',
     'json_cc_file': '<(SHARED_INTERMEDIATE_DIR)/json_gen.cc',
     'uri_cc_file': '<(SHARED_INTERMEDIATE_DIR)/uri_gen.cc',
     'utf8_cc_file': '<(SHARED_INTERMEDIATE_DIR)/utf8_gen.cc',
@@ skipping 290 matching lines @@
           ],
           'message': 'Generating ''<(snapshot_cc_file)'' file.'
         },
       ]
     },
     {
       # dart binary with a snapshot of corelibs built in.
       'target_name': 'dart',
       'type': 'executable',
       'dependencies': [
-        'libdart',
+        'libdart_export',
         'libdart_builtin',
         'generate_snapshot_file',
       ],
       'include_dirs': [
         '..',
       ],
       'sources': [
         'main.cc',
         'builtin_nolib.cc',
         '<(snapshot_cc_file)',
@@ skipping 72 matching lines @@
       ],
       'conditions': [
         ['OS=="win"', {
           'link_settings': {
             'libraries': [ '-lws2_32.lib', '-lRpcrt4.lib', '-llibeay32MT.lib' ],
           },
         }],
       ],
     },
   ],
+  'conditions': [
+    ['OS=="linux"', {
+      'targets': [
+        {
+          'target_name': 'test_extension',
+          'type': 'shared_library',
+          'dependencies': [
+          ],
+          'include_dirs': [
+            '.',
+          ],
+          'sources': [
+            'test_extension_linux.cc',
+          ],
+          'defines': [
+            'DART_SHARED_LIB',
+          ],
+        },
+      ],
+    }],
+  ],
 }
+