Implement fromEnvironment on bool, int and String

runtime/lib/integers_patch.dart

Index: runtime/lib/integers_patch.dart
diff --git a/runtime/lib/integers_patch.dart b/runtime/lib/integers_patch.dart
index fab603f03eca71b21c3b7fe088aeb40adcaa6f9e..f50dc4bc05192fd0f01e5669a6a1c2a676d3e084 100644
--- a/runtime/lib/integers_patch.dart
+++ b/runtime/lib/integers_patch.dart
@@ -87,6 +87,10 @@ patch class int {
     return _slowParse(source, radix, onError);
   }
 
+  /* patch */ const factory int.fromEnvironment(String name,
+                                                {int defaultValue: 0})
+      native "Integer_fromEnvironment";
+
   static int _slowParse(String source, int radix, int onError(String str)) {
     if (source is! String) throw new ArgumentError(source);
     if (radix is! int) throw new ArgumentError("Radix is not an integer");