Implement fromEnvironment on bool, int and String

tests/corelib/bool_from_environment_default_value_test.dart

Index: tests/corelib/bool_from_environment_default_value_test.dart
diff --git a/tests/corelib/bool_from_environment_default_value_test.dart b/tests/corelib/bool_from_environment_default_value_test.dart
new file mode 100644
index 0000000000000000000000000000000000000000..82acf265a02706f223b871cec972d5d3df45f495
--- /dev/null
+++ b/tests/corelib/bool_from_environment_default_value_test.dart
@@ -0,0 +1,12 @@
+// 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 "package:expect/expect.dart";
+
+main() {
+  Expect.isNull(const bool.fromEnvironment('NOT_FOUND'));
+  Expect.isTrue(const bool.fromEnvironment('NOT_FOUND', defaultValue: true));
+  Expect.isFalse(const bool.fromEnvironment('NOT_FOUND', defaultValue: false));
+  Expect.isNull(const bool.fromEnvironment('NOT_FOUND', defaultValue: null));
+}