[dartdev] Make directory cleanup more resilient on Windows.

Processes on Windows can take longer to exit, taking longer for directories they use to become available for deletion. Accommodate this potentially lengthy by trying several times to delete temp directories before failing the test.

Fixes #47700
TEST=run_test on Windows

Change-Id: Id73d6ba3ff981ed59c89ab833f5775eff5375ae6
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/226980
Reviewed-by: Ben Konyi <bkonyi@google.com>
Commit-Queue: Alexander Aprelev <aam@google.com>

Author: aam

pkg/dartdev/test/utils.dart

@@ -97,8 +97,17 @@ dev_dependencies:
     _process?.kill();
     await _process?.exitCode;
     _process = null;
-    if (dir.existsSync()) {
-      dir.deleteSync(recursive: true);
+    int deleteAttempts = 5;
+    while (dir.existsSync()) {
+      try {
+        dir.deleteSync(recursive: true);
+      } catch (e) {
+        if ((--deleteAttempts) <= 0) {
+          rethrow;
+        }
+        await Future.delayed(Duration(milliseconds: 500));
+        print('Got $e while deleting $dir. Trying again...');
+      }
     }
   }