- Implement a first cut for const String.env in the VM to allow

sdk/lib/core/bool.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.
 
 part of dart.core;
 
 /**
  * The reserved words [:true:] and [:false:] denote objects that are the only
  * instances of this class.
  *
  * It is a compile-time error for a class to attempt to extend or implement
  * bool.
  */
 class bool {
   factory bool._uninstantiable() {
     throw new UnsupportedError(
         "class bool cannot be instantiated");
   }
 
   /**
    * Returns [:"true":] if the receiver is [:true:], or [:"false":] if the
    * receiver is [:false:].
    */
   String toString() {
     return this ? "true" : "false";
   }
+
+  /**
+   * Returns the boolean value of the given environment variable [name].
+   * The [defaultValue] is returned if [name] is not present in the environment
+   * or if its value is not a boolean.
+   */
+  external const factory bool.fromEnvironment(String name,
+                                             {bool defaultValue: false});
 }