fixes #40, extension methods for primitive types

tool/input_sdk/private/js_number.dart

Index: tool/input_sdk/private/js_number.dart
diff --git a/tool/input_sdk/private/js_number.dart b/tool/input_sdk/private/js_number.dart
index 6bc999a4239d7f1593466a32c4441323f871b3fa..4d891f2937739bf3109141dab47d9f0ba362de23 100644
--- a/tool/input_sdk/private/js_number.dart
+++ b/tool/input_sdk/private/js_number.dart
@@ -341,6 +341,9 @@ class JSNumber extends Interceptor implements num {
  * while we want to treat `2.0` as an integer for some operations, its
  * interceptor should answer `true` to `is double`.
  */
+// TODO(jmesserly): for dev_compiler all numbers will get `int` members at
+// runtime for dynamic dispatch. We can fix by checking it at dispatch time.
+@JsPeerInterface(name: 'Number')
 class JSInt extends JSNumber implements int, double {
   const JSInt();