Use a different map to distinguish eval contexts

src/contexts-inl.h

Index: src/contexts-inl.h
diff --git a/src/contexts-inl.h b/src/contexts-inl.h
index cdcb7cf4aa26ccab94fb1e72a3cec6848bc85b67..a51b31257db21b5a6378ad9013ace4c6b46364c8 100644
--- a/src/contexts-inl.h
+++ b/src/contexts-inl.h
@@ -118,6 +118,10 @@ bool Context::IsModuleContext() {
   return map == map->GetHeap()->module_context_map();
 }
 
+bool Context::IsEvalContext() {
+  Map* map = this->map();
+  return map == map->GetHeap()->eval_context_map();
+}
 
 bool Context::IsScriptContext() {
   Map* map = this->map();