Refactor Future constructors.

pkg/scheduled_test/lib/src/descriptor/file_descriptor.dart

 // Copyright (c) 2013, 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 descriptor.file;
 
 import 'dart:async';
 import 'dart:io';
 import 'dart:math' as math;
 import 'dart:utf';
@@ skipping 45 matching lines @@
       if (orderedIterableEquals(contents, actualContents)) return;
       if (isBinary) {
         // TODO(nweiz): show a hex dump here if the data is small enough.
         throw "File '$name' didn't contain the expected binary data.";
       }
       throw _textMismatchMessage(textContents,
           new String.fromCharCodes(actualContents));
     });
   }
 
-  Stream<List<int>> read() => new Future.immediate(contents).asStream();
+  Stream<List<int>> read() => new Future.value(contents).asStream();
 
   String describe() => name;
 
   String _textMismatchMessage(String expected, String actual) {
     final expectedLines = expected.split('\n');
     final actualLines = actual.split('\n');
 
     var results = [];
 
     // Compare them line by line to see which ones match.
@@ skipping 18 matching lines @@
         }
       }
     }
 
     return "File '$name' should contain:\n"
         "${prefixLines(expected)}\n"
         "but actually contained:\n"
         "${results.join('\n')}";
   }
 }