[test] Tweak vm/dart/issue_31959_31960_test to avoid timeout

Test vm/dart/issue_31959_31960_test is very slow in interpreter-only
debug mode and sometimes times out.

This change reduces sample list created in the test by 10x
(from 100 000 000 to 10 000 000 items). Also, static types are added to
improve its performance in interpreter-only mode.

Change-Id: Ib8eef973252d42120a0a365919f293a12a03b07e
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/107447
Reviewed-by: Alexander Aprelev <aam@google.com>
Commit-Queue: Alexander Markov <alexmarkov@google.com>
diff --git a/runtime/tests/vm/dart/issue_31959_31960_test.dart b/runtime/tests/vm/dart/issue_31959_31960_test.dart
index 3990fb6..fddff48 100644
--- a/runtime/tests/vm/dart/issue_31959_31960_test.dart
+++ b/runtime/tests/vm/dart/issue_31959_31960_test.dart
@@ -10,7 +10,7 @@
 import 'package:async_helper/async_helper.dart' show asyncStart, asyncEnd;
 import 'package:expect/expect.dart';
 
-Uint8List generateSampleList(final size) {
+Uint8List generateSampleList(final int size) {
   final list = Uint8List(size);
   for (int i = 0; i < size; i++) {
     list[i] = i % 243;
@@ -18,7 +18,7 @@
   return list;
 }
 
-void validateReceivedList(final expectedSize, final list) {
+void validateReceivedList(final int expectedSize, final list) {
   Expect.equals(expectedSize, list.length);
   // probe few elements
   for (int i = 0; i < list.length; i += max<num>(1, expectedSize ~/ 1000)) {
@@ -56,7 +56,7 @@
 
 main() async {
   asyncStart();
-  int bignum = 100 * 1000 * 1000;
+  int bignum = 10 * 1000 * 1000;
   await testSend(false, bignum, 1); // none
   await testSend(true, bignum, 1); // 31959tr
   await testSend(false, bignum, 1); // 31960