Handle defered handling of exceptions (where the exception is thrown before the

corelib/src/implementation/future_implementation.dart

Index: corelib/src/implementation/future_implementation.dart
diff --git a/corelib/src/implementation/future_implementation.dart b/corelib/src/implementation/future_implementation.dart
index 47c1e5d8c07ac628f806556c1f7e1b1e0de3fc1c..dcbaa014253c1985ca6abc9266986f6d7b5b5f25 100644
--- a/corelib/src/implementation/future_implementation.dart
+++ b/corelib/src/implementation/future_implementation.dart
@@ -91,7 +91,13 @@ class FutureImpl<T> implements Future<T> {
   }
 
   void handleException(void onException(Object exception)) {
-    _exceptionHandlers.add(onException);
+    if (_exception !== null) {
+      if (!_exceptionHandled) {
+        _exceptionHandled = onException(exception);
+      }
+    } else {
+      _exceptionHandlers.add(onException);
+    }
   }
 
   void _complete() {