Add a mode to completely deserialize scope chains

src/background-parsing-task.cc

 // Copyright 2014 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.
 
 #include "src/background-parsing-task.h"
 #include "src/debug/debug.h"
 
 namespace v8 {
 namespace internal {
 
@@ skipping 43 matching lines @@
   // background thread.
   uintptr_t stack_limit =
       reinterpret_cast<uintptr_t>(&stack_limit) - stack_size_ * KB;
   source_->parser->set_stack_limit(stack_limit);
 
   // Nullify the Isolate temporarily so that the background parser doesn't
   // accidentally use it.
   Isolate* isolate = source_->info->isolate();
   source_->info->set_isolate(nullptr);
 
+  source_->parser->DeserializeScopeChain(
+      source_->info.get(), Handle<Context>::null(),
+      Scope::DeserializationMode::kDeserializeOffHeap);
   source_->parser->ParseOnBackground(source_->info.get());
 
   if (script_data_ != nullptr) {
     source_->cached_data.reset(new ScriptCompiler::CachedData(
         script_data_->data(), script_data_->length(),
         ScriptCompiler::CachedData::BufferOwned));
     script_data_->ReleaseDataOwnership();
     delete script_data_;
     script_data_ = nullptr;
   }
   source_->info->set_isolate(isolate);
 }
 }  // namespace internal
 }  // namespace v8