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

DEPS

Index: DEPS
diff --git a/DEPS b/DEPS
index 8b2d8d86a6095148954953361885ce7e2b52c2f0..2f037c536960feadb3278bc1798d4245d197345a 100644
--- a/DEPS
+++ b/DEPS
@@ -370,8 +370,8 @@ hooks = [
       '--no_resume',
       '--bucket',
       'dart-dependencies',
-      '-d',
-      '-r',
+      '--recursive',
+      '--directory',
       Var('dart_root') + '/tools/testing/bin',
     ],
   },
@@ -384,10 +384,25 @@ hooks = [
       '--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",
+    ],
+  },
 ]