Add Future.of that calls a function and captures the result

tests/lib/async/future_test.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library future_test;
 
 import 'dart:async';
 import 'dart:isolate';
 
 testImmediate() {
   final future = new Future<String>.immediate("42");
   var port = new ReceivePort();
   future.then((x) {
     Expect.equals("42", x);
     port.close();
   });
 }
 
+testOf() {
+  compare(func) {
+    // Compare the results of the following two futures.
+    Future f1 = new Future.of(func);
+    Future f2 = new Future.immediate(null).then((_) => func());
+    f2.catchError((_){});  // I'll get the error later.
+    f1.then((v1) { f2.then((v2) { Expect.equals(v1, v2); }); },
+            onError: (e1) {
+              f2.then((_) { Expect.fail("Expected error"); },
+                      onError: (e2) {
+                         Expect.equals(e1.error, e2.error);
+                      });
+            });
+  }
+  Future val = new Future.immediate(42);
+  Future err1 = new Future.immediateError("Error")..catchError((_){});
+  Future err2 = new Future.immediateError(new AsyncError("AsyncError"))..catchError((_){});
+  compare(() => 42);
+  compare(() => val);
+  compare(() { throw "Flif"; });
+  compare(() { throw new AsyncError("AsyncFlif"); });
+  compare(() => err1);
+  compare(() => err2);
+}
+
 testNeverComplete() {
   final completer = new Completer<int>();
   final future = completer.future;
   future.then((v) => Expect.fails("Value not expected"));
   future.catchError((e) => Expect.fails("Value not expected"));
 }
 
 testComplete() {
   final completer = new Completer<int>();
   final future = completer.future;
@@ skipping 523 matching lines @@
   future.then((v) => new Future.immediateError("Fehler"))
         .then((v) { Expect.fail("unreachable!"); }, onError: (e) {
           Expect.equals("Fehler", e.error);
           port.close();
         });
   completer.complete(21);
 }
 
 main() {
   testImmediate();
+  testOf();
   testNeverComplete();
 
   testComplete();
   testCompleteWithSuccessHandlerBeforeComplete();
   testCompleteWithSuccessHandlerAfterComplete();
   testCompleteManySuccessHandlers();
   testCompleteWithAsyncError();
 
   testException();
   testExceptionHandler();
@@ skipping 20 matching lines @@
   testFutureThenThrowsAsync();
   testFutureCatchThrowsAsync();
   testFutureWhenThrowsAsync();
   testFutureCatchRethrowsAsync();
 
   testChainedFutureValue();
   testChainedFutureValueDelay();
   testChainedFutureError();
 }
 
+