[dart2js] Repro for issue 52170.

Type inference is not tracking the type of 'local' correctly through the switch statement into the inner return. The same code without the for loop does work correctly though.

Change-Id: I0b1b4741e4ff17c22dec3383defb412f5fff0836
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/298980
Reviewed-by: Stephen Adams <sra@google.com>
Reviewed-by: Mayank Patke <fishythefish@google.com>
Commit-Queue: Nate Biggs <natebiggs@google.com>

pkg/compiler/test/inference/data/issue_52170.dart

@@ -0,0 +1,32 @@
+// Copyright (c) 2023, 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.
+
+/*member: getInt:[exact=JSUInt31]*/
+int get getInt => 42;
+
+// TODO(http://dartbug.com/52170): Return type should include int. The return
+// within the loop can and will be invoked with local = 3.
+/*member: foo:Value([null|exact=JSString], value: "hello")*/
+foo() {
+  dynamic local = 3;
+  for (int i = 0;
+      i /*invoke: [subclass=JSPositiveInt]*/ < 10;
+      i /*invoke: [subclass=JSPositiveInt]*/ ++) {
+    switch (getInt) {
+      case 42:
+        break;
+      default:
+        local = 'hello';
+    }
+    if (i /*invoke: [subclass=JSPositiveInt]*/ > 5) {
+      return local;
+    }
+  }
+  return null;
+}
+
+/*member: main:[null]*/
+void main() {
+  foo();
+}