[api] Expose v8::Object::IsApiWrapper

Allow querying whether an object is capable of holding information that
is relevant to the embedder in its embedder fields.

Bug: chromium:999262
Change-Id: Iced1a1cc78142481990d40d91d8e70e6e5518c5b
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1773268Reviewed-by: Adam Klein <adamk@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Adam Klein <adamk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#63463}

include/v8.h

@@ -3785,6 +3785,15 @@ class V8_EXPORT Object : public Value {
    */
   bool IsConstructor();
 
+  /**
+   * True if this object can carry information relevant to the embedder in its
+   * embedder fields, false otherwise. This is generally true for objects
+   * constructed through function templates but also holds for other types where
+   * V8 automatically adds internal fields at compile time, such as e.g.
+   * v8::ArrayBuffer.
+   */
+  bool IsApiWrapper();
+
   /**
    * Call an Object as a function if a callback is set by the
    * ObjectTemplate::SetCallAsFunctionHandler method.

src/api/api.cc

@@ -4713,6 +4713,11 @@ bool v8::Object::IsConstructor() {
   return self->IsConstructor();
 }
 
+bool v8::Object::IsApiWrapper() {
+  auto self = i::Handle<i::JSObject>::cast(Utils::OpenHandle(this));
+  return self->IsApiWrapper();
+}
+
 MaybeLocal<Value> Object::CallAsFunction(Local<Context> context,
                                          Local<Value> recv, int argc,
                                          Local<Value> argv[]) {