Clean up error handling.

dart/tests/compiler/dart2js/deprecated_features_test.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.
 
 // Test that deprecated language features are diagnosed correctly.
 
 import "package:expect/expect.dart";
 import 'dart:async';
 
 import '../../../sdk/lib/_internal/compiler/compiler.dart';
@@ skipping 46 matching lines @@
       "0<#library('test');>::${deprecatedMessage('# tags')}\n"
       "19<part 'part.dart';>::${deprecatedMessage('missing part-of tag')}\n"
       "0<>:/part.dart:info: Note: This file has no part-of tag, but it is being"
       " used as a part.\n"
       "57<()>::${deprecatedMessage('getter parameters')}\n",
       messages.toString());
 }
 
 deprecatedMessage(feature) {
   return
-    "warning: Warning: deprecated language feature, $feature"
+    "warning: Warning: Deprecated language feature, $feature"
     ", will be removed in a future Dart milestone.";
 }
 
 const Map<String, String> TEST_SOURCE =
   const <String, String>{ '': """
 #library('test');
 
 part 'part.dart';
 
 class Foo {
   get x() => null;
 }
 
 main() {
   var a = new Foo();
 }
 """,
     // TODO(ahe): Why isn't this 'part.dart'? Why the leading slash?
     '/part.dart': '',
   };