per file caching (#38869)

https://dart.googlesource.com/external/github.com/flutter/flutter/+/700020fc6bd08f373042b9d1d38747c9b2a32d8c
diff --git a/commits.json b/commits.json
index 62a8400..73449b8 100644
--- a/commits.json
+++ b/commits.json
@@ -1,5 +1,5 @@
 {
   "external/github.com/flutter/engine":"df31dba49f0a23bafb34b4f614074e991ee813a7",
-  "external/github.com/flutter/flutter":"bbcfdea101b8649c931ac0770d365439defc3ad0",
+  "external/github.com/flutter/flutter":"700020fc6bd08f373042b9d1d38747c9b2a32d8c",
   "sdk":"3865187956cad51bc7065d30beb8ab89702b7953"
 }
\ No newline at end of file