Implement fromEnvironment on bool, int and String

sdk/lib/core/string.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;
 
 /**
  * A sequence of characters.
  *
  * A string can be either single or multiline. Single line strings are
@@ skipping 107 matching lines @@
    *
    * Creating a String with half of a surrogate pair is legal but generally
    * discouraged.
    */
   factory String.fromCharCode(int charCode) {
     List<int> charCodes = new List<int>.filled(1, charCode);
     return new String.fromCharCodes(charCodes);
   }
 
   /**
+   * Returns the string for the given environment variable [name] or
+   * [defaultValue] if [name] is not present.
+   */
+  external const factory String.fromEnvironment(String name,
+                                                {String defaultValue});
+
+  /**
    * Gets the character (as a single-code-unit [String]) at the given [index].
    *
    * The returned string represents exactly one UTF-16 code unit, which may be
    * half of a surrogate pair. A single member of a surrogate pair is an
    * invalid UTF-16 string:
    *
    *     var clef = '\u{1D11E}';
    *     // These represent invalid UTF-16 strings.
    *     clef[0].codeUnits;      // [0xD834]
    *     clef[1].codeUnits;      // [0xDD1E]
@@ skipping 511 matching lines @@
         _position = position - 1;
         _currentCodePoint = _combineSurrogatePair(prevCodeUnit, codeUnit);
         return true;
       }
     }
     _position = position;
     _currentCodePoint = codeUnit;
     return true;
   }
 }