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 ce2c97be753f774d04bfa22cbd47707d6ded1b60..a68da02fe7fb1956f42e3460ea86e35f088bc1d9 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();