Work around issue 9252 in scheduled_test.

pkg/http/test/utils.dart

Index: pkg/http/test/utils.dart
diff --git a/pkg/http/test/utils.dart b/pkg/http/test/utils.dart
index 6bbe139a7adbc856d7ec3b1b9603f67a225342c3..15909782edc5d39ca1d5a8a9d492e74d746c21d1 100644
--- a/pkg/http/test/utils.dart
+++ b/pkg/http/test/utils.dart
@@ -138,6 +138,41 @@ String cleanUpLiteral(String text) {
   return lines.join('\n');
 }
 
+// TODO(nweiz): Remove this when issue 9252 is fixed.
+/// Asynchronously recursively deletes [dir]. Returns a [Future] that completes
+/// when the deletion is done.
+Future deleteDir(String dir) =>
+  _attemptRetryable(() => new Directory(dir).delete(recursive: true));
+
+/// On Windows, we sometimes get failures where the directory is still in use
+/// when we try to do something with it. This is usually because the OS hasn't
+/// noticed yet that a process using that directory has closed. To be a bit
+/// more resilient, we wait and retry a few times.
+///
+/// Takes a [callback] which returns a future for the operation being attempted.
+/// If that future completes with an error, it will slepp and then [callback]
+/// will be invoked again to retry the operation. It will try a few times before
+/// giving up.
+Future _attemptRetryable(Future callback()) {
+  // Only do lame retry logic on Windows.
+  if (Platform.operatingSystem != 'windows') return callback();
+
+  var attempts = 0;
+  makeAttempt(_) {
+    attempts++;
+    return callback().catchError((e) {
+      if (attempts >= 10) {
+        throw 'Could not complete operation. Gave up after $attempts attempts.';
+      }
+
+      return new Future.delayed(new Duration(milliseconds: 500))
+          .then(makeAttempt);
+    });
+  }
+
+  return makeAttempt(null);
+}
+
 /// A matcher that matches JSON that parses to a value that matches the inner
 /// matcher.
 Matcher parse(matcher) => new _Parse(matcher);