Implement constant maps.

frog/leg/lib/js_helper.dart

Index: frog/leg/lib/js_helper.dart
diff --git a/frog/leg/lib/js_helper.dart b/frog/leg/lib/js_helper.dart
index 835ff0a6e7403fc81e0beb4662e10428eb36f3c0..b6ff89060e426cc9a57743f913920daf8c524af4 100644
--- a/frog/leg/lib/js_helper.dart
+++ b/frog/leg/lib/js_helper.dart
@@ -6,6 +6,7 @@
 
 #import('coreimpl.dart');
 
+#source('constant_map.dart');
 #source('date_helper.dart');
 #source('regexp_helper.dart');
 #source('string_helper.dart');
@@ -1368,3 +1369,11 @@ class StackTrace {
   StackTrace(this.stack);
   String toString() => stack != null ? stack : '';
 }
+
+bool jsHasOwnProperty(var jsObject, String property) {
+  return JS('bool', @'$0.hasOwnProperty($1)', jsObject, property);
+}
+
+jsPropertyAccess(var jsObject, String property) {
+  return JS('var', @'$0[$1]', jsObject, property);
+}