[snapshot] do not skip nullptr embedder fields.

R=petermarshall@chromium.org

Bug: chromium:617892
Change-Id: I4077ae567297d18edd6c6748f9f64bbdafb34896
Reviewed-on: https://chromium-review.googlesource.com/616561
Commit-Queue: Yang Guo <yangguo@chromium.org>
Reviewed-by: Peter Marshall <petermarshall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47368}

src/snapshot/partial-serializer.cc

@@ -141,8 +141,6 @@ void PartialSerializer::SerializeEmbedderFields() {
     int embedder_fields_count = obj->GetEmbedderFieldCount();
     for (int i = 0; i < embedder_fields_count; i++) {
       if (obj->GetEmbedderField(i)->IsHeapObject()) continue;
-      // Do not attempt to serialize nullptr embedder fields.
-      if (obj->GetEmbedderField(i) == 0) continue;
 
       StartupData data = serialize_embedder_fields_.callback(
           v8::Utils::ToLocal(obj), i, serialize_embedder_fields_.data);

test/cctest/test-serialize.cc

@@ -597,9 +597,9 @@ v8::StartupData SerializeInternalFields(v8::Local<v8::Object> holder, int index,
   CHECK_EQ(reinterpret_cast<void*>(2016), data);
   InternalFieldData* embedder_field = static_cast<InternalFieldData*>(
       holder->GetAlignedPointerFromInternalField(index));
+  if (embedder_field == nullptr) return {nullptr, 0};
   int size = sizeof(*embedder_field);
   char* payload = new char[size];
-  DCHECK(embedder_field != nullptr);
   // We simply use memcpy to serialize the content.
   memcpy(payload, embedder_field, size);
   return {payload, size};
@@ -609,6 +609,10 @@ std::vector<InternalFieldData*> deserialized_data;
 
 void DeserializeInternalFields(v8::Local<v8::Object> holder, int index,
                                v8::StartupData payload, void* data) {
+  if (payload.raw_size == 0) {
+    holder->SetAlignedPointerInInternalField(index, nullptr);
+    return;
+  }
   CHECK_EQ(reinterpret_cast<void*>(2017), data);
   InternalFieldData* embedder_field = new InternalFieldData{0};
   memcpy(embedder_field, payload.data, payload.raw_size);
@@ -660,6 +664,7 @@ void TypedArrayTestHelper(const char* code,
         v8::DeserializeInternalFieldsCallback(DeserializeInternalFields,
                                               reinterpret_cast<void*>(2017)));
     delete[] blob.data;  // We can dispose of the snapshot blob now.
+    CHECK(deserialized_data.empty());  // We do not expect any embedder data.
     v8::Context::Scope c_scope(context);
     TestInt32Expectations(expectations);
   }