Use FutureOr more and make Future.sync return the resulting Future directly.

tests/lib/async/future_test.dart

Index: tests/lib/async/future_test.dart
diff --git a/tests/lib/async/future_test.dart b/tests/lib/async/future_test.dart
index 5d84ff15f76ab8822f7199fe59cf0823ac746b90..efe66e25c327ffc2c83d7ba7281a801b74a3853c 100644
--- a/tests/lib/async/future_test.dart
+++ b/tests/lib/async/future_test.dart
@@ -994,9 +994,9 @@ void testTypes() {
         new Future<int>.delayed(Duration.ZERO, () => value));
     testType(
         "Future.microtask($value)", new Future<int>.microtask(() => value));
-    testType("Future.sync($value)", new Future<int>.sync(() => value)); // //# 01: ok
-    testType("Future.sync(future($value))", //                             //# 01: continued
-             new Future<int>.sync(() async => new Future.value(value))); //# 01: continued
+    testType("Future.sync($value)", new Future<int>.sync(() => value)); //    //# 01: ok
+    testType("Future.sync(future($value))", //                                //# 01: continued
+             new Future<int>.sync(() async => new Future<int>.value(value))); //# 01: continued
     testType("Future.value($value)", new Future<int>.value(value));
   }
   testType("Completer.future", new Completer<int>().future);