Add a reserved namespace (himBHinitial identifiers) for transformer configuration.

sdk/lib/_internal/pub/test/pubspec_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.
 
 library pubspec_test;
 
 import 'package:unittest/unittest.dart';
 
 import '../lib/src/pubspec.dart';
 import '../lib/src/source.dart';
@@ skipping 177 matching lines @@
           (pubspec) => pubspec.transformers);
       expectPubspecException('transformers: [12]',
           (pubspec) => pubspec.transformers);
     });
 
     test("throws if a transformer's configuration isn't a map", () {
       expectPubspecException('transformers: {pkg: 12}',
           (pubspec) => pubspec.transformers);
     });
 
+    test("throws if a transformer's configuration contains a top-level key "
+        "beginning with a dollar sign", () {
+      expectPubspecException('transformers: {pkg: {\$key: value}}',
+          (pubspec) => pubspec.transformers);
+    });
+
+    test("doesn't throw if a transformer's configuration contains a "
+        "non-top-level key beginning with a dollar sign", () {
+      expectPubspecException('transformers: {pkg: {\$key: value}}',
+          (pubspec) => pubspec.transformers);
+    });
+
     test("allows comment-only files", () {
       var pubspec = new Pubspec.parse('''
 # No external dependencies yet
 # Including for completeness
 # ...and hoping the spec expands to include details about author, version, etc
 # See http://www.dartlang.org/docs/pub-package-manager/ for details
 ''', sources);
       expect(pubspec.version, equals(Version.none));
       expect(pubspec.dependencies, isEmpty);
     });
@@ skipping 32 matching lines @@
             (pubspec) => pubspec.environment);
       });
 
       test("throws if the sdk isn't a valid version constraint", () {
         expectPubspecException('environment: {sdk: "oopies"}',
             (pubspec) => pubspec.environment);
       });
     });
   });
 }