Revert "Make Zone API strong mode clean."

tests/lib/async/run_zoned6_test.dart

Index: tests/lib/async/run_zoned6_test.dart
diff --git a/tests/lib/async/run_zoned6_test.dart b/tests/lib/async/run_zoned6_test.dart
index 906c776f3d6d91a7b28428fe59ea0bb38b0a3e38..491a9391166b6d736d876637a785e5765db0fe54 100644
--- a/tests/lib/async/run_zoned6_test.dart
+++ b/tests/lib/async/run_zoned6_test.dart
@@ -8,19 +8,20 @@ import 'package:async_helper/async_helper.dart';
 
 main() {
   asyncStart();
-  // Ensure that `runZoned`'s onError handles synchronous errors, and throwing
-  // in the error handler at that point (when it is a synchronous error) yields
-  // a synchronous error.
+  // Ensure that `runZoned`'s onError handles synchronous errors but delegates
+  // to the top-level when the handler returns false.
   try {
     runZoned(() {
       throw 0;
     }, onError: (e) {
       Expect.equals(0, e);
-      throw e;  //#01 : ok
+               if (false) //# 01: runtime error
       asyncEnd();
+               throw e; //# 01: runtime error
     });
   } catch (e) {
-    asyncEnd(); return;  //# 01: continued
+    // We should never see an error here.
+    if (false) //# 01: continued
     rethrow;
   }
 }