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

src/messages.h

 // Copyright 2006-2008 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.
 
 // The infrastructure used for (localized) message reporting in V8.
 //
 // Note: there's a big unresolved issue about ownership of the data
 // structures used by this framework.
 
 #ifndef V8_MESSAGES_H_
@@ skipping 165 matching lines @@
   T(OrdinaryFunctionCalledAsConstructor,                                       \
     "Function object that's not a constructor was created with new")           \
   T(PromiseCyclic, "Chaining cycle detected for promise %")                    \
   T(PropertyDescObject, "Property description must be an object: %")           \
   T(PropertyNotFunction, "Property '%' of object % is not a function")         \
   T(ProtoObjectOrNull, "Object prototype may only be an Object or null: %")    \
   T(PrototypeParentNotAnObject,                                                \
     "Class extends value does not have valid prototype property %")            \
   T(ProxyHandlerDeleteFailed,                                                  \
     "Proxy handler % did not return a boolean value from 'delete' trap")       \
-  T(ProxyHandlerNonObject, "Proxy.create called with non-object as handler")   \
+  T(ProxyHandlerNonObject, "Cannot create proxy with non-object as handler")   \
   T(ProxyHandlerReturned, "Proxy handler % returned % from '%' trap")          \
   T(ProxyHandlerTrapMissing, "Proxy handler % has no '%' trap")                \
   T(ProxyHandlerTrapMustBeCallable,                                            \
     "Proxy handler %0 has non-callable '%' trap")                              \
+  T(ProxyIsExtensibleViolatesInvariant,                                        \
+    "Result of trap 'isExtensible' is inconsistent with proxy's target")       \
   T(ProxyNonObjectPropNames, "Trap '%' returned non-object %")                 \
+  T(ProxyPreventExtensionsViolatesInvariant,                                   \
+    "Trap 'preventExtensions' returned true but the proxy's target is "        \
+    "extensible")                                                              \
   T(ProxyPropNotConfigurable,                                                  \
     "Proxy handler % returned non-configurable descriptor for property '%' "   \
     "from '%' trap")                                                           \
   T(ProxyRepeatedPropName, "Trap '%' returned repeated property name '%'")     \
+  T(ProxyRevoked, "Cannot perform '%' on a proxy that has been revoked")       \
   T(ProxyTargetNotExtensible, "Proxy target is not extensible")                \
-  T(ProxyTargetNonObject, "Proxy.% called with non-object as target")          \
+  T(ProxyTargetNonObject, "Proxy target is non-object")                        \
   T(ProxyTargetPropNotConfigurable,                                            \
     "Proxy target property '%' is not configurable")                           \
   T(ProxyTrapFunctionExpected,                                                 \
     "Proxy.createFunction called with non-function for '%' trap")              \
   T(RedefineDisallowed, "Cannot redefine property: %")                         \
   T(RedefineExternalArray,                                                     \
     "Cannot redefine a property of an object with external array elements")    \
   T(ReduceNoInitial, "Reduce of empty array with no initial value")            \
   T(RegExpFlags,                                                               \
     "Cannot supply flags when constructing one RegExp from another")           \
@@ skipping 295 matching lines @@
   static MUST_USE_RESULT MaybeHandle<String> GetStringifiedProperty(
       Isolate* isolate, LookupIterator* property_lookup,
       Handle<String> default_value);
 
   List<Handle<JSObject> > visited_;
 };
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_MESSAGES_H_