Add download of the stable SDK from gcloud to the gclient hooks in DEPS.

DEPS

 # 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.
 
 vars = {
   # The dart_root is the root of our sdk checkout. This is normally
   # simply sdk, but if using special gclient specs it can be different.
   "dart_root": "sdk",
 
   # The svn location to pull out dependencies from
@@ skipping 352 matching lines @@
   },
   {
     'name': 'checked_in_dart_binaries',
     'pattern': '.',
     'action': [
       'download_from_google_storage',
       '--no_auth',
       '--no_resume',
       '--bucket',
       'dart-dependencies',
-      '-d',
-      '-r',
+      '--recursive',
+      '--directory',
       Var('dart_root') + '/tools/testing/bin',
     ],
   },
   {
     'name': 'd8_testing_binaries',
     'pattern': '.',
     'action': [
       'download_from_google_storage',
       '--no_auth',
       '--no_resume',
       '--bucket',
       'dart-dependencies',
-      '-d',
-      '-r',
+      '--recursive',
+      '--directory',
       Var('dart_root') + '/third_party/d8',
     ],
   },
-
+  {
+    "name": "checked_in_dart_sdks",
+    "pattern": ".",
+    "action": [
+      "download_from_google_storage",
+      "--no_auth",
+      "--no_resume",
+      "--bucket",
+      "dart-dependencies",
+      "--recursive",
+      "--auto_platform",
+      "--extract",
+      "--directory",
+      Var('dart_root') + "/tools/sdks",
+    ],
+  },
 ]