Proxies: Make 'with' work, plus minor other fixes

src/objects.cc

Index: src/objects.cc
diff --git a/src/objects.cc b/src/objects.cc
index 241da74c98fe25eee19fdc001fd1cc2098326357..269f8ba4b5f0f281d7f4757f8df897eaa6c70fa2 100644
--- a/src/objects.cc
+++ b/src/objects.cc
@@ -3604,17 +3604,24 @@ MUST_USE_RESULT PropertyAttributes JSProxy::GetPropertyAttributeWithHandler(
 
   // Convert result to PropertyAttributes.
   Handle<String> enum_n = isolate->factory()->InternalizeOneByteString(
-      STATIC_ASCII_VECTOR("enumerable"));
+      STATIC_ASCII_VECTOR("enumerable_"));
   Handle<Object> enumerable(v8::internal::GetProperty(isolate, desc, enum_n));
   if (isolate->has_pending_exception()) return NONE;
   Handle<String> conf_n = isolate->factory()->InternalizeOneByteString(
-      STATIC_ASCII_VECTOR("configurable"));
+      STATIC_ASCII_VECTOR("configurable_"));
   Handle<Object> configurable(v8::internal::GetProperty(isolate, desc, conf_n));
   if (isolate->has_pending_exception()) return NONE;
   Handle<String> writ_n = isolate->factory()->InternalizeOneByteString(
-      STATIC_ASCII_VECTOR("writable"));
+      STATIC_ASCII_VECTOR("writable_"));
   Handle<Object> writable(v8::internal::GetProperty(isolate, desc, writ_n));
   if (isolate->has_pending_exception()) return NONE;
+  if (!writable->BooleanValue()) {
+    Handle<String> set_n = isolate->factory()->InternalizeOneByteString(
+        STATIC_ASCII_VECTOR("set_"));
+    Handle<Object> setter(v8::internal::GetProperty(isolate, desc, set_n));
+    if (isolate->has_pending_exception()) return NONE;
+    writable = isolate->factory()->ToBoolean(!setter->IsUndefined());
+  }
 
   if (configurable->IsFalse()) {
     Handle<String> trap = isolate->factory()->InternalizeOneByteString(