Implement fromEnvironment on bool, int, String in dart2js.

sdk/lib/_internal/compiler/implementation/warnings.dart

Index: sdk/lib/_internal/compiler/implementation/warnings.dart
===================================================================
--- sdk/lib/_internal/compiler/implementation/warnings.dart	(revision 29652)
+++ sdk/lib/_internal/compiler/implementation/warnings.dart	(working copy)
@@ -974,6 +974,9 @@
           "foo(void x) {} main() { foo(null); }",
       ]);
 
+  static const MessageKind NULL_NOT_ALLOWED = const MessageKind(
+      "Error: `null` can't be used here.");
+
   static const MessageKind BEFORE_TOP_LEVEL = const MessageKind(
       "Error: Part header must come before top-level definitions.");