[dart2wasm] Support NullRejectionException.isUndefined

Previously, the implementation worked around boxing limitations
by always setting this field to false. However, because we
control both the callback and the JS code that calls the rejection
function, we can pass more information to the callback to let it
know whether the error was undefined.

Change-Id: Ic19f24ec20d321859eb8184d5c87744f7679cf0c
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/439141
Commit-Queue: Srujan Gaddam <srujzs@google.com>
Reviewed-by: Ömer Ağacan <omersa@google.com>

https://dart.googlesource.com/sdk/+/6f85292b08e4e6e1cd94ad94bdfea2b17248518a

DEPS

diff --git a/DEPS b/DEPS
index f864fb2..d3e665a 100644
--- a/DEPS
+++ b/DEPS
@@ -229,7 +229,7 @@
 ]
 
 deps = {
-  'flutter/engine/src/flutter/third_party/dart': Var('dart_git') + '/sdk' + '@' + 'ee2e81ecd0d476b0a66bb4c1e48305984ee80745',
+  'flutter/engine/src/flutter/third_party/dart': Var('dart_git') + '/sdk' + '@' + '6f85292b08e4e6e1cd94ad94bdfea2b17248518a',
 
   'flutter': Var('flutter_git') + '/mirrors/flutter' + '@' + '17e63958f2d0854ea2d42b218587e024171c4272',
 

commits.json

diff --git a/commits.json b/commits.json
index 926bfca..50f9075 100644
--- a/commits.json
+++ b/commits.json
@@ -1,4 +1,4 @@
 {
   "flutter":"17e63958f2d0854ea2d42b218587e024171c4272",
-  "flutter/engine/src/flutter/third_party/dart":"ee2e81ecd0d476b0a66bb4c1e48305984ee80745"
+  "flutter/engine/src/flutter/third_party/dart":"6f85292b08e4e6e1cd94ad94bdfea2b17248518a"
 }
\ No newline at end of file