Refactor Future constructors.

sdk/lib/_internal/compiler/implementation/source_file_provider.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 source_file_provider;
 
 import 'dart:async';
 import 'dart:uri';
 import 'dart:io';
 import 'dart:utf';
@@ skipping 27 matching lines @@
     String source;
     try {
       source = readAll(uriPathToNative(resourceUri.path));
     } on FileIOException catch (ex) {
       throw 'Error: Cannot read "${relativize(cwd, resourceUri, isWindows)}" '
             '(${ex.osError}).';
     }
     dartCharactersRead += source.length;
     sourceFiles[resourceUri.toString()] =
       new SourceFile(relativize(cwd, resourceUri, isWindows), source);
-    return new Future.immediate(source);
+    return new Future.value(source);
   }
 }
 
 class FormattingDiagnosticHandler {
   final SourceFileProvider provider;
   bool showWarnings = true;
   bool verbose = false;
   bool isAborting = false;
   bool enableColors = false;
   bool throwOnError = false;
@@ skipping 53 matching lines @@
       print(file.getLocationMessage(color(message), begin, end, true, color));
     }
     if (fatal && throwOnError) {
       isAborting = true;
       throw new AbortLeg(message);
     }
   }
 }