Generate snapshot for dartj2s; use it in the SDK.

dart/utils/compiler/compiler.gyp

 # 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': {
     'dart_dir': '../..',
   },
   'targets': [
     {
@@ skipping 27 matching lines @@
             # Unfortunately, there is some strange interaction with
             # GYP so it doesn't work.
             '<(PRODUCT_DIR)',
             '<(EXECUTABLE_PREFIX)dart<(EXECUTABLE_SUFFIX)',
             'dart2js',
             'dart2js_developer',
             'dartdoc',
             '<(dart_dir)',
           ],
         },
+        {
+          'action_name': 'generate_dart2js_snapshot',
+          'inputs': [
+            '<(PRODUCT_DIR)/<(EXECUTABLE_PREFIX)gen_snapshot<(EXECUTABLE_SUFFIX)',
+            '<(PRODUCT_DIR)/<(EXECUTABLE_PREFIX)dart<(EXECUTABLE_SUFFIX)',
+            '../../lib/_internal/libraries.dart',
+            '<!@(["python", "../../tools/list_files.py", "\\.dart$", "../../lib/compiler", "../../runtime/lib"])',
+          ],
+          'outputs': [
+            '<(PRODUCT_DIR)/dart2js.snapshot',
+          ],
+          'action': [
+            '<(PRODUCT_DIR)/<(EXECUTABLE_PREFIX)gen_snapshot<(EXECUTABLE_SUFFIX)',
+            # Note: we don't store the snapshot in the location where
+            # the dart2js script is looking for it.  The motivation
+            # for that is to support an incremental development model
+            # for dart2js compiler engineers.  However, we install the
+            # snapshot in the proper location when building the SDK.
+            '--script_snapshot=<(PRODUCT_DIR)/dart2js.snapshot',
+            '../../lib/compiler/implementation/dart2js.dart',
+          ],
+        },
       ],
     },
   ],
 }