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

sdk/lib/async/future_impl.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.
 
 part of dart.async;
 
 deprecatedFutureValue(_FutureImpl future) =>
   future._isComplete ? future._resultOrListeners : null;
 
 
@@ skipping 286 matching lines @@
       _addListener(future._asListener());
     } else if (_hasValue) {
       future._setValue(_resultOrListeners);
     } else {
       assert(_hasError);
       _clearUnhandledError();
       future._setError(_resultOrListeners);
     }
   }
 
-  _FutureListener _asListener() => new _FutureListener.wrap(this);
-}
-
-/**
- * Transforming future base class.
- *
- * A transforming future is itself a future and a future listener.
- * Subclasses override [_sendValue]/[_sendError] to intercept
- * the results of a previous future.
- */
-abstract class _TransformFuture<S, T> extends _FutureImpl<T>
-                                      implements _FutureListener<S> {
-  // _FutureListener implementation.
-  _FutureListener _nextListener;
-
-  void _sendValue(S value);
-
-  void _sendError(AsyncError error);
-
-  void _subscribeTo(_FutureImpl future) {
-    future._addListener(this);
-  }
-
   /**
-   * Helper function to hand the result of transforming an incoming event.
+   * Helper function to handle the result of transforming an incoming event.
    *
    * If the result is itself a [Future], this future is linked to that
    * future's output. If not, this future is completed with the result.
    */
   void _setOrChainValue(var result) {
     if (result is Future) {
       // Result should be a Future<T>.
       if (result is _FutureImpl) {
         _FutureImpl chainFuture = result;
         chainFuture._chain(this);
         return;
       } else {
         Future future = result;
         future.then(_setValue,
                     onError: _setError);
         return;
       }
     } else {
       // Result must be of type T.
       _setValue(result);
     }
   }
+
+  _FutureListener _asListener() => new _FutureListener.wrap(this);
+}
+
+/**
+ * Transforming future base class.
+ *
+ * A transforming future is itself a future and a future listener.
+ * Subclasses override [_sendValue]/[_sendError] to intercept
+ * the results of a previous future.
+ */
+abstract class _TransformFuture<S, T> extends _FutureImpl<T>
+                                      implements _FutureListener<S> {
+  // _FutureListener implementation.
+  _FutureListener _nextListener;
+
+  void _sendValue(S value);
+
+  void _sendError(AsyncError error);
+
+  void _subscribeTo(_FutureImpl future) {
+    future._addListener(this);
+  }
 }
 
 /** The onValue and onError handlers return either a value or a future */
 typedef dynamic _FutureOnValue<T>(T value);
 typedef dynamic _FutureOnError(AsyncError error);
 /** Test used by [Future.catchError] to handle skip some errors. */
 typedef bool _FutureErrorTest(var error);
 /** Used by [WhenFuture]. */
 typedef _FutureAction();
 
@@ skipping 157 matching lines @@
   Future catchError(function(AsyncError error), {bool test(var error)}) {
     return _future.catchError(function, test: test);
   }
 
   Future<T> whenComplete(action()) {
     return _future.whenComplete(action);
   }
 
   Stream<T> asStream() => new Stream.fromFuture(_future);
 }