Implement fromEnvironment on bool, int and String

tests/standalone/from_environment_int_script.dart

Index: tests/standalone/from_environment_int_script.dart
diff --git a/tests/standalone/from_environment_int_script.dart b/tests/standalone/from_environment_int_script.dart
new file mode 100644
index 0000000000000000000000000000000000000000..f42853640bef94ce331db691c576f8c88c48fe7e
--- /dev/null
+++ b/tests/standalone/from_environment_int_script.dart
@@ -0,0 +1,14 @@
+// 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.
+
+import "dart:convert";
+import "dart:io";
+
+main(List<String> args) {
+  var result = new Map();
+  result['a'] = const int.fromEnvironment('a', defaultValue: null);
+  result['b'] = const int.fromEnvironment('b');
+  result['c'] = const int.fromEnvironment('c');
+  stdout.write(JSON.encode(result));
+}