Implement fromEnvironment on bool, int and String

sdk/lib/core/bool.dart

Index: sdk/lib/core/bool.dart
diff --git a/sdk/lib/core/bool.dart b/sdk/lib/core/bool.dart
index 6c7797fc4cb3be57f6fefaef74996aee1095a03e..c4348b7117300303f2ebc949c16a18562749f707 100644
--- a/sdk/lib/core/bool.dart
+++ b/sdk/lib/core/bool.dart
@@ -12,10 +12,11 @@ part of dart.core;
  * bool.
  */
 class bool {
-  factory bool._uninstantiable() {
-    throw new UnsupportedError(
-        "class bool cannot be instantiated");
-  }
+  /**
+   * Returns the boolean for the given environment variable [name] or
+   * [defaultValue] if [name] is not present.
+   */
+  external const factory bool.fromEnvironment(String name, {bool defaultValue});

[Lasse Reichstein Nielsen, 2013/10/31 06:55:38]

I still think the default is silly, but if it is there, it should at least
default to false, not null.
The most common use should be to check for the presence of a -Dfoo=true, and you
don't want null there.

 
   /**
    * Returns [:"true":] if the receiver is [:true:], or [:"false":] if the