[api] Add a CHECK to investigate crbug.com/713699

BUG=chromium:713699

Cq-Include-Trybots: master.tryserver.chromium.linux:linux_chromium_rel_ng
Change-Id: Ibe30fe7922a421af1596070fde4519bd2f870c4e
Reviewed-on: https://chromium-review.googlesource.com/525535
Commit-Queue: Camillo Bruni <cbruni@chromium.org>
Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#45728}

src/api.cc

@@ -6479,6 +6479,11 @@ Local<Context> NewContext(
     v8::MaybeLocal<Value> global_object, size_t context_snapshot_index,
     v8::DeserializeInternalFieldsCallback embedder_fields_deserializer) {
   i::Isolate* isolate = reinterpret_cast<i::Isolate*>(external_isolate);
+  // TODO(jkummerow): This is for crbug.com/713699. Remove it if it doesn't
+  // fail.
+  // Sanity-check that the isolate is initialized and usable.
+  CHECK(isolate->builtins()->Illegal()->IsCode());
+
   TRACE_EVENT_CALL_STATS_SCOPED(isolate, "v8", "V8.NewContext");
   LOG_API(isolate, Context, New);
   i::HandleScope scope(isolate);