Move microtask queueing logic from JavaScript to C++

src/heap.cc

 // Copyright 2012 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 "v8.h"
 
 #include "accessors.h"
 #include "api.h"
 #include "bootstrapper.h"
 #include "codegen.h"
@@ skipping 2879 matching lines @@
 
   set_undefined_cell(*factory->NewCell(factory->undefined_value()));
 
   // The symbol registry is initialized lazily.
   set_symbol_registry(undefined_value());
 
   // Allocate object to hold object observation state.
   set_observation_state(*factory->NewJSObjectFromMap(
       factory->NewMap(JS_OBJECT_TYPE, JSObject::kHeaderSize)));
 
-  // Allocate object to hold object microtask state.
-  set_microtask_state(*factory->NewJSObjectFromMap(
-      factory->NewMap(JS_OBJECT_TYPE, JSObject::kHeaderSize)));
+  // Microtask queue uses the empty fixed array as a sentinel for "empty".
+  // Number of queued microtasks stored in Isolate::pending_microtask_count().
+  set_microtask_queue(empty_fixed_array());
 
   set_frozen_symbol(*factory->NewPrivateSymbol());
   set_nonexistent_symbol(*factory->NewPrivateSymbol());
   set_elements_transition_symbol(*factory->NewPrivateSymbol());
   set_uninitialized_symbol(*factory->NewPrivateSymbol());
   set_megamorphic_symbol(*factory->NewPrivateSymbol());
   set_observed_symbol(*factory->NewPrivateSymbol());
 
   Handle<SeededNumberDictionary> slow_element_dictionary =
       SeededNumberDictionary::New(isolate(), 0, TENURED);
@@ skipping 3553 matching lines @@
       static_cast<int>(object_sizes_last_time_[index]));
   CODE_AGE_LIST_COMPLETE(ADJUST_LAST_TIME_OBJECT_COUNT)
 #undef ADJUST_LAST_TIME_OBJECT_COUNT
 
   OS::MemCopy(object_counts_last_time_, object_counts_, sizeof(object_counts_));
   OS::MemCopy(object_sizes_last_time_, object_sizes_, sizeof(object_sizes_));
   ClearObjectStats();
 }
 
 } }  // namespace v8::internal