Expose IsConstructor to the C++ API

BUG=v8:4993
R=verwaest@chromium.org
LOG=y

Review-Url: https://codereview.chromium.org/1964433002
Cr-Commit-Position: refs/heads/master@{#36107}

include/v8.h

@@ -2967,6 +2967,11 @@ class V8_EXPORT Object : public Value {
    */
   bool IsCallable();
 
+  /**
+   * True if this object is a constructor.
+   */
+  bool IsConstructor();
+
   /**
    * Call an Object as a function if a callback is set by the
    * ObjectTemplate::SetCallAsFunctionHandler method.

src/api.cc

@@ -4363,6 +4363,10 @@ bool v8::Object::IsCallable() {
   return self->IsCallable();
 }
 
+bool v8::Object::IsConstructor() {
+  auto self = Utils::OpenHandle(this);
+  return self->IsConstructor();
+}
 
 MaybeLocal<Value> Object::CallAsFunction(Local<Context> context,
                                          Local<Value> recv, int argc,

test/cctest/test-api.cc

@@ -11101,6 +11101,7 @@ THREADED_TEST(FunctionRemovePrototype) {
   Local<v8::FunctionTemplate> t1 = v8::FunctionTemplate::New(isolate);
   t1->RemovePrototype();
   Local<v8::Function> fun = t1->GetFunction(context.local()).ToLocalChecked();
+  CHECK(!fun->IsConstructor());
   CHECK(context->Global()->Set(context.local(), v8_str("fun"), fun).FromJust());
   CHECK(!CompileRun("'prototype' in fun")
              ->BooleanValue(context.local())