frog await: allow errors after the await within try-catch blocks.

frog/tests/await/src/NestedTryCatch4Test.dart

+// Copyright (c) 2011, 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.
+
+// Await within a nested try-catch block, throw happens on await, inner catch
+// has priority.
+
+#import("await_test_helper.dart");
+
+class E1 implements Exception {
+  const E1([msg=null]);
+}
+
+awaitAndThrow(Exception ex) {
+  try {
+    try {
+      final f = errorOf(ex);
+      final t = await f;
+      return 0;
+    } catch (E1 e) {
+      return 1;
+    }
+  } catch (E1 e) {
+    return 2;
+  }
+}
+
+main() {
+  int t = await awaitAndThrow(const E1());
+  Expect.equals(1, t);
+}