Spelling fixes e to i.

tests/lib/async/zone_bind_callback_unary_test.dart

Index: tests/lib/async/zone_bind_callback_unary_test.dart
diff --git a/tests/lib/async/zone_bind_callback_unary_test.dart b/tests/lib/async/zone_bind_callback_unary_test.dart
index 3f315e312db6b8dc50abd0c1615412794fc2b8e6..19155abc214e579679806fbe5be14444dce0f34b 100644
--- a/tests/lib/async/zone_bind_callback_unary_test.dart
+++ b/tests/lib/async/zone_bind_callback_unary_test.dart
@@ -36,7 +36,7 @@ main() {
   Expect.isFalse(identical(fun, bound));
 
   // It is legal to invoke the callback in a different zone. This is, of course,
-  // etremely discouraged.
+  // extremely discouraged.
   var result = bound(399);
   Expect.equals(498, result);
   Expect.equals(499, restoredValue);