Implement fromEnvironment on bool, int, String in dart2js.

tests/corelib/bool_from_environment_test.dart

Index: tests/corelib/bool_from_environment_test.dart
===================================================================
--- tests/corelib/bool_from_environment_test.dart	(revision 0)
+++ tests/corelib/bool_from_environment_test.dart	(revision 0)
@@ -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.
+// SharedOptions=-Da=true -Db=false
+
+import "package:expect/expect.dart";
+
+main(List<String> args) {
+  Expect.isTrue(const bool.fromEnvironment('a'));
+  Expect.isFalse(const bool.fromEnvironment('b'));
+  Expect.isFalse(const bool.fromEnvironment('c'));
+}