Add a flag to prohibit plurals/genders that don't take up the whole string.

pkg/intl/test/message_extraction/failed_extraction_test.dart

 // 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 failed_extraction_test;
 
 import "message_extraction_test.dart";
 import "dart:io";
 import "package:unittest/unittest.dart";
 
 main() {
   test("Expect warnings but successful extraction", () {
     runTestWithWarnings(warningsAreErrors: false, expectedExitCode: 0);
   });
 }
 
-void runTestWithWarnings({bool warningsAreErrors, int expectedExitCode}) {
+const defaultFiles =
+    const ["sample_with_messages.dart", "part_of_sample_with_messages.dart"];
+
+void runTestWithWarnings({bool warningsAreErrors, int expectedExitCode,
+  bool embeddedPlurals: true, List<String> sourceFiles: defaultFiles}) {
 
   void verify(ProcessResult result) {
     try {
       expect(result.exitCode, expectedExitCode);
     } finally {
       deleteGeneratedFiles();
     }
   }
 
   copyFilesToTempDirectory();
   var program = asTestDirPath("../../bin/extract_to_arb.dart");
   var args = ["--output-dir=$tempDir"];
   if (warningsAreErrors) {
     args.add('--warnings-are-errors');
   }
-  var files = [asTempDirPath("sample_with_messages.dart"), asTempDirPath(
-      "part_of_sample_with_messages.dart"),];
+  if (!embeddedPlurals) {
+    args.add('--no-embedded-plurals');
+  }
+  var files = sourceFiles.map(asTempDirPath).toList();
   var allArgs = [program]
       ..addAll(args)
       ..addAll(files);
   var callback = expectAsync(verify);
   run(null, allArgs).then(callback);
 }