Populate subbuild deps for engine_v2 builder recipe

LED run: https://luci-milo.appspot.com/raw/build/logs.chromium.org/flutter/led/flutter-try-builder_chops-service-accounts.iam.gserviceaccount.com/9439283d87bf8375c527c7b2ed06e648f4f497d0a7353917e32ab7a9919dd972/+/build.proto

Change-Id: Ib6c9cdc47bfffc6bac71175a9b784befdeb4f442
Reviewed-on: https://flutter-review.googlesource.com/c/recipes/+/41121
Reviewed-by: Godofredo Contreras <godofredoc@google.com>
Commit-Queue: Keyong Han <keyonghan@google.com>
diff --git a/recipes/engine_v2/builder.py b/recipes/engine_v2/builder.py
index db7c23a..05096f0 100644
--- a/recipes/engine_v2/builder.py
+++ b/recipes/engine_v2/builder.py
@@ -147,9 +147,9 @@
   ninja_tool = {
       "ninja": api.build_util.build,
   }
-  deps = api.properties.get('dependencies', [])
-  api.flutter_deps.required_deps(env, env_prefixes, deps)
   build = api.properties.get('build')
+  deps = build.get('dependencies', [])
+  api.flutter_deps.required_deps(env, env_prefixes, deps)
   api.flutter_bcid.report_stage('compile')
   gn = build.get('gn')
   if gn: