[builtins] Only create constants table if serializing

Since we currently only fill the constants table if we're serializing,
we should only create & finalize the table in that case. Otherwise,
leave it initialized to empty_fixed_array.

Cq-Include-Trybots: luci.v8.try:v8_linux64_fyi_rel_ng
Bug: v8:6666
Change-Id: I6ecbfac9dc9a9dac7ff0f11331be09b1cbfb4c18
Reviewed-on: https://chromium-review.googlesource.com/948490Reviewed-by: Sigurd Schneider <sigurds@chromium.org>
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51727}

src/builtins/constants-table-builder.cc

@@ -32,6 +32,8 @@ uint32_t BuiltinsConstantsTableBuilder::AddObject(Handle<Object> object) {
   // Not yet finalized.
   DCHECK_EQ(isolate_->heap()->empty_fixed_array(),
             isolate_->heap()->builtins_constants_table());
+
+  DCHECK(isolate_->serializer_enabled());
 #endif
 
   uint32_t* maybe_key = map_.Find(object);
@@ -68,6 +70,7 @@ void BuiltinsConstantsTableBuilder::Finalize() {
 
   DCHECK_EQ(isolate_->heap()->empty_fixed_array(),
             isolate_->heap()->builtins_constants_table());
+  DCHECK(isolate_->serializer_enabled());
 
   DCHECK_LT(0, map_.size());
   Handle<FixedArray> table =

src/isolate.cc

@@ -3050,7 +3050,10 @@ bool Isolate::Init(StartupDeserializer* des) {
     // Terminate the partial snapshot cache so we can iterate.
     partial_snapshot_cache_.push_back(heap_.undefined_value());
 #ifdef V8_EMBEDDED_BUILTINS
-    builtins_constants_table_builder_ = new BuiltinsConstantsTableBuilder(this);
+    if (serializer_enabled()) {
+      builtins_constants_table_builder_ =
+          new BuiltinsConstantsTableBuilder(this);
+    }
 #endif
   }
 
@@ -3085,7 +3088,7 @@ bool Isolate::Init(StartupDeserializer* des) {
     setup_delegate_->SetupInterpreter(interpreter_);
 
 #ifdef V8_EMBEDDED_BUILTINS
-    if (create_heap_objects) {
+    if (create_heap_objects && serializer_enabled()) {
       builtins_constants_table_builder_->Finalize();
       delete builtins_constants_table_builder_;
       builtins_constants_table_builder_ = nullptr;