patch from issue 9360020

corelib/src/implementation/future_implementation.dart

 // Copyright 2011 Google Inc. All Rights Reserved.
 // Dart core library.
 
 /**
  * Thrown if client tries to obtain value or exception
  * before a future has completed.
  */
 class FutureNotCompleteException implements Exception {
   FutureNotCompleteException() {}
   String toString() => "Exception: future has not been completed";
@@ skipping 37 matching lines @@
   /**
    * Exception handlers waiting for exceptions.
    */
   final List<Function> _exceptionHandlers;
 
   FutureImpl() : _listeners = new List(), _exceptionHandlers = new List() {
     _isComplete = false;
     _exceptionHandled = false;
   }
 
+  FutureImpl.immediate(T value) : this() {
+    _setValue(value);
+  }
+
   T get value() {
     if (!isComplete) {
       throw new FutureNotCompleteException();
     }
     if (_exception !== null) {
       throw _exception;
     }
     return _value;
   }
 
@@ skipping 59 matching lines @@
     if (exception === null) {
       // null is not a legal value for the exception of a Future
       throw new IllegalArgumentException(null);
     }
     if (_isComplete) {
       throw new FutureAlreadyCompleteException();
     }
     _exception = exception;
     _complete();
   }
+
+  Future transform(Function transformation) {
+    final completer = new Completer();
+    handleException((e) {
+      completer.completeException(e);
+      return true;
+    });
+    then((v) {
+      var transformed = null;
+      try {
+        transformed = transformation(v);
+      } catch (final e) {
+        completer.completeException(e);
+        return;
+      }
+      completer.complete(transformed);
+    });
+    return completer.future;
+  }
+
+  Future chain(Function transformation) {
+    final completer = new Completer();
+    handleException((e) {
+      completer.completeException(e);
+      return true;
+    });
+    then((v) {
+      var future = null;
+      try {
+        future = transformation(v);
+      } catch (final e) {
+        completer.completeException(e);
+        return;
+      }
+      future.handleException((e) {
+        completer.completeException(e);
+        return true;
+      });
+      future.then((b) => completer.complete(b));
+    });
+    return completer.future;
+  }
 }
 
 class CompleterImpl<T> implements Completer<T> {
 
   final FutureImpl<T> _futureImpl;
 
   CompleterImpl() : _futureImpl = new FutureImpl() {}
 
   Future<T> get future() {
     return _futureImpl;
   }
 
   void complete(T value) {
     _futureImpl._setValue(value);
   }
 
   void completeException(var exception) {
     _futureImpl._setException(exception);
   }
 }