[infra] Add back generate_buildfiles.py to gclient hooks

Omitting this was a little fragile. We can add it back following the
fix in https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1255446

Change-Id: Idfa0a08674bc1ea7ef19d7c9a96e17e6da293297
Reviewed-on: https://dart-review.googlesource.com/c/84280
Reviewed-by: Alexander Thomas <athom@google.com>
Commit-Queue: Zach Anderson <zra@google.com>
diff --git a/DEPS b/DEPS
index 4e7c835..ec830d0 100644
--- a/DEPS
+++ b/DEPS
@@ -490,4 +490,8 @@
     'pattern': '.',
     'action': ['python', 'sdk/build/vs_toolchain.py', 'update'],
   },
+  {
+    "pattern": ".",
+    "action": ["python", Var("dart_root") + "/tools/generate_buildfiles.py"],
+  },
 ]