Migration: Add IndexExpression support to FixBuilder.

Change-Id: I870047d12304c70cfe89e64d4864cc1809b7e4ac
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/121408
Commit-Queue: Paul Berry <paulberry@google.com>
Reviewed-by: Mike Fairhurst <mfairhurst@google.com>

https://dart.googlesource.com/sdk/+/1e3cbd434472a79e73313795a55f094a1e9df0d4
diff --git a/commits.json b/commits.json
index 79ee77a..2ea3737 100644
--- a/commits.json
+++ b/commits.json
@@ -1,5 +1,5 @@
 {
   "external/github.com/flutter/engine":"75c400ea6d3429d9bf2ffafe03401207c82bee9a",
   "external/github.com/flutter/flutter":"3fea2838df051e99b2f72127a7d950287e522d0b",
-  "sdk":"5594981c2a03a8f5587f488ee5245d6038d21a7a"
+  "sdk":"1e3cbd434472a79e73313795a55f094a1e9df0d4"
 }
\ No newline at end of file