Implement IsConstructor() abstract operation

src/runtime/runtime-function.cc

Index: src/runtime/runtime-function.cc
diff --git a/src/runtime/runtime-function.cc b/src/runtime/runtime-function.cc
index 608cc9548423a34543b739c6a6d85e0571200579..62d5513e542782ed8b4d285d1130556e9789f0a1 100644
--- a/src/runtime/runtime-function.cc
+++ b/src/runtime/runtime-function.cc
@@ -326,6 +326,34 @@ RUNTIME_FUNCTION(Runtime_SetNativeFlag) {
 }
 
 
+RUNTIME_FUNCTION(Runtime_IsConstructor) {
+  HandleScope handles(isolate);
+  RUNTIME_ASSERT(args.length() == 1);
+
+  CONVERT_ARG_HANDLE_CHECKED(Object, object, 0);
+
+  // TODO(caitp): implement this in a better/simpler way, allow inlining via TF
+  if (object->IsJSFunction()) {
+    Handle<JSFunction> func = Handle<JSFunction>::cast(object);
+    bool should_have_prototype = func->should_have_prototype();
+    if (func->shared()->bound()) {
+      Handle<FixedArray> bound_args =
+          Handle<FixedArray>(FixedArray::cast(func->function_bindings()));
+      Handle<Object> bound_function(
+          JSReceiver::cast(bound_args->get(JSFunction::kBoundFunctionIndex)),
+          isolate);
+      if (bound_function->IsJSFunction()) {
+        Handle<JSFunction> bound = Handle<JSFunction>::cast(bound_function);
+        DCHECK(!bound->shared()->bound());
+        should_have_prototype = bound->should_have_prototype();
+      }
+    }
+    return isolate->heap()->ToBoolean(should_have_prototype);
+  }
+  return isolate->heap()->false_value();
+}
+
+
 RUNTIME_FUNCTION(Runtime_SetInlineBuiltinFlag) {
   SealHandleScope shs(isolate);
   RUNTIME_ASSERT(args.length() == 1);