src: make BaseObject::is_snapshotable virtual

Use a virtual function in order to save space (8 bytes per instance
on 64-bit platforms) and in order to be consistent with the other
methods on BaseObject.

PR-URL: nodejs#37539
Reviewed-By: Gerhard Stöbich <deb2001-github@yahoo.de>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Darshan Sen <raisinten@gmail.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

src/base_object.h

@@ -158,8 +158,7 @@ class BaseObject : public MemoryRetainer {
 
   virtual inline void OnGCCollect();
 
-  bool is_snapshotable() const { return is_snapshotable_; }
-  void set_is_snapshotable(bool val) { is_snapshotable_ = val; }
+  virtual inline bool is_snapshotable() const { return false; }
 
  private:
   v8::Local<v8::Object> WrappedObject() const override;
@@ -209,7 +208,6 @@ class BaseObject : public MemoryRetainer {
 
   Environment* env_;
   PointerData* pointer_data_ = nullptr;
-  bool is_snapshotable_ = false;
 };
 
 // Global alias for FromJSObject() to avoid churn.

src/node_snapshotable.cc

@@ -16,7 +16,6 @@ SnapshotableObject::SnapshotableObject(Environment* env,
                                        Local<Object> wrap,
                                        EmbedderObjectType type)
     : BaseObject(env, wrap), type_(type) {
-  set_is_snapshotable(true);
 }
 
 const char* SnapshotableObject::GetTypeNameChars() const {

src/node_snapshotable.h

@@ -90,6 +90,7 @@ class SnapshotableObject : public BaseObject {
   virtual void PrepareForSerialization(v8::Local<v8::Context> context,
                                        v8::SnapshotCreator* creator) = 0;
   virtual InternalFieldInfo* Serialize(int index) = 0;
+  bool is_snapshotable() const override { return true; }
   // We'll make sure that the type is set in the constructor
   EmbedderObjectType type() { return type_; }