[proxies] Make Object.prototype.isPrototypeOf work with proxies.

src/objects-inl.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 //
 // Review notes:
 //
 // - The use of macros in these inline functions may seem superfluous
 // but it is absolutely needed to make sure gcc generates optimal
 // code. gcc is not happy when attempting to inline too deep.
 //
@@ skipping 1179 matching lines @@
 
 MaybeHandle<Object> Object::GetPrototype(Isolate* isolate,
                                          Handle<Object> receiver) {
   // We don't expect access checks to be needed on JSProxy objects.
   DCHECK(!receiver->IsAccessCheckNeeded() || receiver->IsJSObject());
   Handle<Context> context(isolate->context());
   if (receiver->IsAccessCheckNeeded() &&
       !isolate->MayAccess(context, Handle<JSObject>::cast(receiver))) {
     return isolate->factory()->null_value();
   }
-  if (receiver->IsJSProxy()) {
-    return JSProxy::GetPrototype(Handle<JSProxy>::cast(receiver));
-  }
   PrototypeIterator iter(isolate, receiver,
                          PrototypeIterator::START_AT_RECEIVER);
   do {
-    iter.AdvanceIgnoringProxies();
-    if (PrototypeIterator::GetCurrent(iter)->IsJSProxy()) {
-      return PrototypeIterator::GetCurrent(iter);
-    }
+    if (!iter.AdvanceFollowingProxies()) return MaybeHandle<Object>();
   } while (!iter.IsAtEnd(PrototypeIterator::END_AT_NON_HIDDEN));
   return PrototypeIterator::GetCurrent(iter);
 }
 
 
 MaybeHandle<Object> Object::GetProperty(Isolate* isolate, Handle<Object> object,
                                         const char* name,
                                         LanguageMode language_mode) {
   Handle<String> str = isolate->factory()->InternalizeUtf8String(name);
   return GetProperty(object, str, language_mode);
@@ skipping 6636 matching lines @@
 #undef WRITE_INT64_FIELD
 #undef READ_BYTE_FIELD
 #undef WRITE_BYTE_FIELD
 #undef NOBARRIER_READ_BYTE_FIELD
 #undef NOBARRIER_WRITE_BYTE_FIELD
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_OBJECTS_INL_H_