Generators return boxed values

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index 4b5b51d9d90e2363c3542c877a5489f8ddb7203d..ca7c6a97145c25291eda93bf88ed0ae234f317cc 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -6421,6 +6421,12 @@ class JSGeneratorObject: public JSObject {
   // Resume mode, for use by runtime functions.
   enum ResumeMode { SEND, THROW };
 
+  // Yielding from a generator returns an object with the following inobject
+  // properties.  See Context::iterator_result_map() for the map.
+  static const int kResultValuePropertyIndex = 0;
+  static const int kResultDonePropertyIndex = 1;
+  static const int kResultPropertyCount = 2;
+
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(JSGeneratorObject);
 };