Revert "Make Zone API strong mode clean."

tests/lib/async/run_zoned9_test.dart

Index: tests/lib/async/run_zoned9_test.dart
diff --git a/tests/lib/async/run_zoned9_test.dart b/tests/lib/async/run_zoned9_test.dart
index 1ab97953cdb4bcb3c84c068a27bdc5d755643304..67e389425b24d82e1ef83cd28b9d3c9d2efcde89 100644
--- a/tests/lib/async/run_zoned9_test.dart
+++ b/tests/lib/async/run_zoned9_test.dart
@@ -24,11 +24,13 @@ main() {
       Expect.equals(0, e);
       Expect.isTrue(sawInnerHandler);
       // If we are waiting for an error, don't asyncEnd, but let it time out.
-      throw e;  //# 01: ok
+      if (false) //# 01: runtime error
       asyncEnd();
+      throw e; //  //# 01: continued
     });
   } catch (e) {
-    asyncEnd(); return;  //# 01: continued
+    // We should never see an error here.
+    if (false) //  //# 01: continued
     rethrow;
   }
 }