Avoid flaking in message_extraction tests by doing everything in a temp directory

pkg/intl/test/message_extraction/foo_messages_all.dart

-/**
- * DO NOT EDIT. This is code generated via pkg/intl/generate_localized.dart
- * This is a library that looks up messages for specific locales by
- * delegating to the appropriate library.
- */
+// Copyright (c) 2014, 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 messages_all;
+library keep_the_static_analysis_from_complaining;
 
-import 'dart:async';
-import 'package:intl/message_lookup_by_library.dart';
-import 'package:intl/src/intl_helpers.dart';
-import 'package:intl/intl.dart';
-
-import 'foo_messages_de_DE.dart' as messages_de_DE;
-import 'foo_messages_fr.dart' as messages_fr;
-
-
-MessageLookupByLibrary _findExact(localeName) {
-  switch (localeName) {
-    case 'de_DE' : return messages_de_DE.messages;
-    case 'fr' : return messages_fr.messages;
-    default: return null;
-  }
-}
-
-/** User programs should call this before using [localeName] for messages.*/
-Future initializeMessages(String localeName) {
-  initializeInternalMessageLookup(() => new CompositeMessageLookup());
-  messageLookup.addLocale(localeName, _findGeneratedMessagesFor);
-  // TODO(alanknight): Restore once Issue 12824 is fixed.
-  // var lib = deferredLibraries[localeName];
-  // return lib == null ? new Future.value(false) : lib.load();
-  return new Future.value(true);
-}
-
-MessageLookupByLibrary _findGeneratedMessagesFor(locale) {
-  var actualLocale = Intl.verifiedLocale(locale, (x) => _findExact(x) != null,
-      onFailure: (_) => null);
-  if (actualLocale == null) return null;
-  return _findExact(actualLocale);
-}
+initializeMessages(_) => throw new UnimplementedError(
+    "This entire file is only here to make the static"
+    " analysis happy. It will be generated during actual tests.");