Implement for-in loop for proxies.

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index a3c9cc2d0a945b06b449d488929053abe7bae702..6ee527d312dfeb520b9f5c5c09ead507876d78fe 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -1365,6 +1365,9 @@ class JSReceiver: public HeapObject {
                                           StrictModeFlag strict_mode,
                                           bool check_prototype);
 
+  // Tests for the fast common case for property enumeration.
+  bool IsSimpleEnum();
+
   // Returns the class name ([[Class]] property in the specification).
   String* class_name();
 
@@ -1617,9 +1620,6 @@ class JSObject: public JSReceiver {
   MUST_USE_RESULT MaybeObject* DeleteProperty(String* name, DeleteMode mode);
   MUST_USE_RESULT MaybeObject* DeleteElement(uint32_t index, DeleteMode mode);
 
-  // Tests for the fast common case for property enumeration.
-  bool IsSimpleEnum();
-
   inline void ValidateSmiOnlyElements();
 
   // Makes sure that this object can contain non-smi Object as elements.