Fix context unchaining (issue 5991015).

tests/language/src/Context2Test.dart

+// Copyright (c) 2012, 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.
+// Dart test for capturing.
+
+// Regression test for issue 5991015.
+
+class V {
+
+  foofoo(x) { return x; }
+
+  hoop(input, n) {
+    while (n-- > 0) {
+      Expect.equals(5, input);
+      continue;  // This continue statement must properly unchain the context.
+      switch (input) {
+        case 3:
+          var values = foofoo;
+          readPacked(() => values(input));
+      }
+    }
+  }
+}
+
+main() {
+  new V().hoop(5, 3);
+}