implement private members, fixes #74

test/codegen/expect/typed_data/typed_data.js

Index: test/codegen/expect/typed_data/typed_data.js
diff --git a/test/codegen/expect/typed_data/typed_data.js b/test/codegen/expect/typed_data/typed_data.js
index 55b71930f70a50ef6b20fcd7a354eac4eaa8f48f..49427d86539254bfb61cfeeef12d2055b7f0d0db 100644
--- a/test/codegen/expect/typed_data/typed_data.js
+++ b/test/codegen/expect/typed_data/typed_data.js
@@ -5,9 +5,10 @@ var typed_data;
   }
   class TypedData extends dart.Object {
   }
+  let _littleEndian = Symbol('_littleEndian');
   class Endianness extends dart.Object {
-    Endianness$_(_littleEndian) {
-      this._littleEndian = _littleEndian;
+    Endianness$_($_littleEndian) {
+      this[_littleEndian] = $_littleEndian;
     }
   }
   dart.defineNamedConstructor(Endianness, '_');