Handle function proxies as getters/setters.

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index d9c7a82276cfed24c89d8474ed3e4bbbb03a1afa..5288df4968ce2760797a44e148822694ee8ffd28 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -835,6 +835,9 @@ class MaybeObject BASE_EMBEDDED {
   V(AccessCheckNeeded)                         \
   V(JSGlobalPropertyCell)                      \
 
+
+class JSReceiver;
+
 // Object is the abstract superclass for all classes in the
 // object hierarchy.
 // Object does not use any virtual functions to avoid the
@@ -859,6 +862,7 @@ class Object : public MaybeObject {
 #undef DECLARE_STRUCT_PREDICATE
 
   INLINE(bool IsSpecObject());
+  INLINE(bool IsSpecFunction());
 
   // Oddball testing.
   INLINE(bool IsUndefined());
@@ -911,7 +915,7 @@ class Object : public MaybeObject {
                                                       String* name,
                                                       Object* handler);
   MUST_USE_RESULT MaybeObject* GetPropertyWithDefinedGetter(Object* receiver,
-                                                            JSFunction* getter);
+                                                            JSReceiver* getter);
 
   inline MaybeObject* GetElement(uint32_t index);
   // For use when we know that no exception can be thrown.
@@ -1571,7 +1575,7 @@ class JSObject: public JSReceiver {
       Object* value,
       JSObject* holder,
       StrictModeFlag strict_mode);
-  MUST_USE_RESULT MaybeObject* SetPropertyWithDefinedSetter(JSFunction* setter,
+  MUST_USE_RESULT MaybeObject* SetPropertyWithDefinedSetter(JSReceiver* setter,
                                                             Object* value);
   MUST_USE_RESULT MaybeObject* SetPropertyWithInterceptor(
       String* name,