[dart2js] Add regression test for https://dart-review.googlesource.com/c/sdk/+/225320

Change-Id: Iff348b9ce13ea249b8c63f8c0952cd446ad5cb7d
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/243528
Commit-Queue: Mayank Patke <fishythefish@google.com>
Reviewed-by: Sigmund Cherem <sigmund@google.com>

Author: fishythefish

pkg/compiler/test/inference/data/late_field.dart

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+// Copyright (c) 2022, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:compiler/src/util/testing.dart';
+
+/*member: Foo.:[exact=Foo]*/
+class Foo {
+  /*member: Foo._#Foo#x:[sentinel|exact=JSUInt31]*/
+  /*member: Foo.x:[exact=JSUInt31]*/
+  late int /*[exact=Foo]*/ /*update: [exact=Foo]*/ x = 42;
+}
+
+/*member: main:[null]*/
+void main() {
+  makeLive(test(Foo()));
+}
+
+@pragma('dart2js:noInline')
+/*member: test:[exact=JSUInt31]*/
+int test(Foo /*[exact=Foo]*/ foo) => foo. /*[exact=Foo]*/ x;

tests/web/late_no_inlining_test.dart

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+// Copyright (c) 2022, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// dart2jsOptions=--disable-inlining
+
+import 'package:expect/expect.dart';
+
+// Tests to ensure that narrowing type information does not discard late
+// sentinel values unintentionally.
+
+class Foo {
+  late int bar = 42;
+  late final int baz = 1729;
+}
+
+void main() {
+  final foo = Foo();
+  Expect.equals(42, foo.bar);
+  Expect.equals(1729, foo.baz);
+}