Use shared positionalFieldIndex() to check for INVALID_FIELD_NAME_POSITIONAL.

Change-Id: I368a49b8304304f09e835c690e3f91b84dd1a688
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/260962
Commit-Queue: Konstantin Shcheglov <scheglov@google.com>
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>

https://dart.googlesource.com/sdk/+/cfddeee68e0cf7451a2eee1a9fbbff8a8d9c0b92
diff --git a/commits.json b/commits.json
index 8c9a794..dc03319 100644
--- a/commits.json
+++ b/commits.json
@@ -1,5 +1,5 @@
 {
   "external/github.com/flutter/engine":"01fca5e2f52548f299405fa5145003ffd3aa39bf",
   "external/github.com/flutter/flutter":"a1c86ef476fe5dbf689ac50cb3ac5618b7fe8e10",
-  "sdk":"94507d65020bdcd9a6651d29848a2864ca9cc2be"
+  "sdk":"cfddeee68e0cf7451a2eee1a9fbbff8a8d9c0b92"
 }
\ No newline at end of file