[proxies] Implement [[PreventExtensions]] and [[IsExtensible]].

src/builtins.cc

 // 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.
 
 #include "src/builtins.h"
 
 #include "src/api.h"
 #include "src/api-natives.h"
 #include "src/arguments.h"
 #include "src/base/once.h"
@@ skipping 1603 matching lines @@
   DCHECK_EQ(2, args.length());
   Handle<Object> target = args.at<Object>(1);
 
   if (!target->IsJSReceiver()) {
     THROW_NEW_ERROR_RETURN_FAILURE(
         isolate, NewTypeError(MessageTemplate::kCalledOnNonObject,
                               isolate->factory()->NewStringFromAsciiChecked(
                                   "Reflect.isExtensible")));
   }
 
-  // TODO(neis): For now, we ignore proxies.  Once proxies are fully
-  // implemented, do something like the following:
-  /*
-  Maybe<bool> maybe = JSReceiver::IsExtensible(
-      Handle<JSReceiver>::cast(target));
-  if (!maybe.IsJust()) return isolate->heap()->exception();
-  return *isolate->factory()->ToBoolean(maybe.FromJust());
-  */
-
-  if (target->IsJSObject()) {
-    return *isolate->factory()->ToBoolean(
-        JSObject::IsExtensible(Handle<JSObject>::cast(target)));
-  }
-  return *isolate->factory()->false_value();
+  Maybe<bool> result =
+      JSReceiver::IsExtensible(Handle<JSReceiver>::cast(target));
+  MAYBE_RETURN(result, isolate->heap()->exception());
+  return *isolate->factory()->ToBoolean(result.FromJust());
 }
 
 
 // ES6 section 26.1.12 Reflect.preventExtensions
 BUILTIN(ReflectPreventExtensions) {
   HandleScope scope(isolate);
   DCHECK_EQ(2, args.length());
   Handle<Object> target = args.at<Object>(1);
 
   if (!target->IsJSReceiver()) {
     THROW_NEW_ERROR_RETURN_FAILURE(
         isolate, NewTypeError(MessageTemplate::kCalledOnNonObject,
                               isolate->factory()->NewStringFromAsciiChecked(
                                   "Reflect.preventExtensions")));
   }
 
   Maybe<bool> result = JSReceiver::PreventExtensions(
       Handle<JSReceiver>::cast(target), Object::DONT_THROW);
-  return result.IsJust() ? *isolate->factory()->ToBoolean(result.FromJust())
-                         : isolate->heap()->exception();
+  MAYBE_RETURN(result, isolate->heap()->exception());
+  return *isolate->factory()->ToBoolean(result.FromJust());
 }
 
 
 // ES6 section 26.1.13 Reflect.set
 BUILTIN(ReflectSet) {
   HandleScope scope(isolate);
   Handle<Object> undef = isolate->factory()->undefined_value();
   Handle<Object> target = args.length() > 1 ? args.at<Object>(1) : undef;
   Handle<Object> key = args.length() > 2 ? args.at<Object>(2) : undef;
   Handle<Object> value = args.length() > 3 ? args.at<Object>(3) : undef;
@@ skipping 721 matching lines @@
 BUILTIN_LIST_C(DEFINE_BUILTIN_ACCESSOR_C)
 BUILTIN_LIST_A(DEFINE_BUILTIN_ACCESSOR_A)
 BUILTIN_LIST_H(DEFINE_BUILTIN_ACCESSOR_H)
 BUILTIN_LIST_DEBUG_A(DEFINE_BUILTIN_ACCESSOR_A)
 #undef DEFINE_BUILTIN_ACCESSOR_C
 #undef DEFINE_BUILTIN_ACCESSOR_A
 
 
 }  // namespace internal
 }  // namespace v8