Change package scheduled_test to throw TestFailures rather than strings.

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:convert';
 import 'dart:io';
 import 'dart:math' as math;
@@ skipping 41 matching lines @@
     return new File(path.join(parent, name)).writeAsBytes(contents);
   }, "creating file '$name'");
 
   Future validate([String parent]) =>
     schedule(() => validateNow(parent), "validating file '$name'");
 
   Future validateNow([String parent]) {
     if (parent == null) parent = defaultRoot;
     var fullPath = path.join(parent, name);
     if (!new File(fullPath).existsSync()) {
-      throw "File not found: '$fullPath'.";
+      fail("File not found: '$fullPath'.");
     }
 
     return new File(fullPath).readAsBytes().then(_validateNow);
   }
 
   // TODO(nweiz): rather than setting up an inheritance chain, just store a
   // Matcher for validation. This would require better error messages from the
   // matcher library, though.
   /// A function that throws an error if [binaryContents] doesn't match the
   /// expected contents of the descriptor.
   void _validateNow(List<int> binaryContents);
 
   Stream<List<int>> read() => new Future.value(contents).asStream();
 
   String describe() => name;
 }
 
 class _BinaryFileDescriptor extends FileDescriptor {
   _BinaryFileDescriptor(String name, List<int> contents)
       : super._(name, contents);
 
   Future _validateNow(List<int> actualContents) {
     if (orderedIterableEquals(contents, actualContents)) return null;
     // TODO(nweiz): show a hex dump here if the data is small enough.
-    throw "File '$name' didn't contain the expected binary data.";
+    fail("File '$name' didn't contain the expected binary data.");
   }
 }
 
 class _StringFileDescriptor extends FileDescriptor {
   _StringFileDescriptor(String name, String contents)
       : super._(name, UTF8.encode(contents));
 
   Future _validateNow(List<int> actualContents) {
     if (orderedIterableEquals(contents, actualContents)) return null;
     throw _textMismatchMessage(textContents,
@@ skipping 42 matching lines @@
 
   _MatcherFileDescriptor(String name, this._matcher, {bool isBinary})
       : _isBinary = isBinary == true ? true : false,
         super._(name, <int>[]);
 
   void _validateNow(List<int> actualContents) =>
       expect(
           _isBinary ? actualContents : new String.fromCharCodes(actualContents),
           _matcher);
 }