[d8 Workers] Throw when calling Worker constructor without new

src/d8.cc

Index: src/d8.cc
diff --git a/src/d8.cc b/src/d8.cc
index ddef1def632d33b6454a4467a00bda3e8aefa7a4..d55faabe8bcc414624f485a9af2c432516185dd6 100644
--- a/src/d8.cc
+++ b/src/d8.cc
@@ -699,6 +699,11 @@ void Shell::WorkerNew(const v8::FunctionCallbackInfo<v8::Value>& args) {
     return;
   }
 
+  if (!args.IsConstructCall()) {
+    Throw(args.GetIsolate(), "Worker must be constructed with new");
+    return;
+  }
+
   {
     base::LockGuard<base::Mutex> lock_guard(workers_mutex_.Pointer());
     // Initialize the internal field to NULL; if we return early without