Create pre-frozen change records for Object.observe

src/bootstrapper.cc

Index: src/bootstrapper.cc
diff --git a/src/bootstrapper.cc b/src/bootstrapper.cc
index 762c4f9962716b477224c59e76418d7e3db7132f..c37fe57b6a04eb692212e4c5ba3f49ac370b3560 100644
--- a/src/bootstrapper.cc
+++ b/src/bootstrapper.cc
@@ -1830,6 +1830,60 @@ bool Genesis::InstallNatives() {
     native_context()->set_regexp_result_map(*initial_map);
   }
 
+  // Should be flag-guarded with FLAG_harmony_observation, but can't due to
+  // context snapshotting.
+  {
+    Handle<Map> change_record_map =
+        factory()->NewMap(JS_OBJECT_TYPE, JSChangeRecord::kSize);
+    change_record_map->set_constructor(native_context()->object_function());
+    change_record_map->set_non_instance_prototype(false);
+    change_record_map->set_prototype(
+        native_context()->initial_object_prototype());
+
+    Handle<DescriptorArray> descriptors = factory()->NewDescriptorArray(0, 4);
+    DescriptorArray::WhitenessWitness witness(*descriptors);
+    change_record_map->set_instance_descriptors(*descriptors);
+
+    PropertyAttributes attrs =
+        static_cast<PropertyAttributes>(READ_ONLY | DONT_DELETE);
+    {
+      FieldDescriptor field(
+          heap()->type_symbol(), JSChangeRecord::kTypeIndex, attrs);
+      change_record_map->AppendDescriptor(&field, witness);
+    }
+    {
+      FieldDescriptor field(
+          heap()->object_symbol(), JSChangeRecord::kObjectIndex, attrs);
+      change_record_map->AppendDescriptor(&field, witness);
+    }
+    {
+      FieldDescriptor field(
+          heap()->name_symbol(), JSChangeRecord::kNameIndex, attrs);
+      change_record_map->AppendDescriptor(&field, witness);
+    }
+
+    change_record_map->set_inobject_properties(4);
+    change_record_map->set_pre_allocated_property_fields(3);
+    change_record_map->set_unused_property_fields(1);
+
+    change_record_map->set_is_extensible(false);
+
+    native_context()->set_change_record_map(*change_record_map);
+
+    // Create a different map for change records with an oldValue property.
+    {
+      FieldDescriptor field(
+          heap()->oldvalue_symbol(), JSChangeRecord::kOldValueIndex, attrs);
+      MaybeObject* maybe_map = change_record_map->CopyAddDescriptor(
+          &field, OMIT_TRANSITION);
+      if (!maybe_map->ToHandle(&change_record_map, isolate())) return false;
+    }
+    change_record_map->set_inobject_properties(4);
+    change_record_map->set_pre_allocated_property_fields(4);
+    change_record_map->set_unused_property_fields(0);
+    native_context()->set_change_record_oldvalue_map(*change_record_map);
+  }
+
 #ifdef VERIFY_HEAP
   builtins->Verify();
 #endif