feat(http): refactor library to work in dart

Mostly internal refactoring needed to make ts2dart and DartAnalyzer happy.

Fixes #2415

modules/angular2/src/facade/lang.dart

@@ -11,6 +11,8 @@ class Math {
   static double random() => _random.nextDouble();
 }
 
+int ENUM_INDEX(value) => value.index;
+
 class CONST {
   const CONST();
 }