Put a snapshot of pub in the SDK.

sdk/lib/_internal/pub/pub.gyp

+# Copyright (c) 2013, 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': 'pub',
+      'type': 'none',
+      'dependencies': [
+        '../../../../runtime/dart-runtime.gyp:dart',
+      ],
+      'actions': [
+        {
+          'action_name': 'generate_pub_snapshot',
+          'inputs': [
+            '<(PRODUCT_DIR)/<(EXECUTABLE_PREFIX)dart<(EXECUTABLE_SUFFIX)',
+            '<!@(["python", "../../../../tools/list_files.py", "\\.dart$", "."])',
+            '../libraries.dart',
+            '<!@(["python", "../../../../tools/list_files.py", "\\.dart$", "../compiler"])',
+            '<!@(["python", "../../../../tools/list_files.py", "\\.dart$", "../../../../pkg"])',
+          ],
+          'outputs': [
+            '<(SHARED_INTERMEDIATE_DIR)/pub.dart.snapshot',
+          ],
+          'action': [
+            '<(PRODUCT_DIR)/<(EXECUTABLE_PREFIX)dart<(EXECUTABLE_SUFFIX)',
+            '--package-root=<(PRODUCT_DIR)/packages/',
+            '--generate-script-snapshot=<(SHARED_INTERMEDIATE_DIR)/pub.dart.snapshot',
+            'bin/pub.dart',
+          ],
+        },
+      ],
+    },
+  ],
+}