Disable implicit casts but keep dynamic casts when NNBD enabled

Change-Id: Ia0a3271c9137bc8c7fa4cdbd469cf93d9453b69c
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/103405
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
Reviewed-by: Paul Berry <paulberry@google.com>
Commit-Queue: Mike Fairhurst <mfairhurst@google.com>

https://dart.googlesource.com/sdk/+/704446d159a76c4f538800b36dc1a0276053fd18
diff --git a/commits.json b/commits.json
index 8e8a081..f51a9ab 100644
--- a/commits.json
+++ b/commits.json
@@ -1,5 +1,5 @@
 {
   "external/github.com/flutter/engine":"ee6a9c40492e54a0ae160293900d9e3b42b725d7",
   "external/github.com/flutter/flutter":"552e74770da213b4d81a19bcbc525e1253c88753",
-  "sdk":"49262365dc2981549889103d033a15b8f6ccbb7b"
+  "sdk":"704446d159a76c4f538800b36dc1a0276053fd18"
 }
\ No newline at end of file