Revert "Make Zone API strong mode clean."

sdk/lib/async/future.dart

Index: sdk/lib/async/future.dart
diff --git a/sdk/lib/async/future.dart b/sdk/lib/async/future.dart
index 5a3d177f74de58fb8209a207acf7e6388058f4c8..eb5fa8b58ad808855a54955a98f6c41d5ee3f80b 100644
--- a/sdk/lib/async/future.dart
+++ b/sdk/lib/async/future.dart
@@ -519,7 +519,7 @@ abstract class Future<T> {
     // context of all the previous iterations' callbacks.
     // This avoids, e.g., deeply nested stack traces from the stack trace
     // package.
-    nextIteration = Zone.current.bindUnaryCallbackGuarded((bool keepGoing) {
+    nextIteration = Zone.current.bindUnaryCallback((bool keepGoing) {
       while (keepGoing) {
         FutureOr<bool> result;
         try {
@@ -537,7 +537,7 @@ abstract class Future<T> {
         keepGoing = result;
       }
       doneSignal._complete(null);
-    });
+    }, runGuarded: true);
     nextIteration(true);
     return doneSignal;
   }