Better support for 'polymorphic' JS and external arrays

src/x64/macro-assembler-x64.h

Index: src/x64/macro-assembler-x64.h
diff --git a/src/x64/macro-assembler-x64.h b/src/x64/macro-assembler-x64.h
index 4c177205b6be4f143933f751678641b9dbc14f52..82c331301c6cd67091c6f8cadf2809ae1e6eb9c9 100644
--- a/src/x64/macro-assembler-x64.h
+++ b/src/x64/macro-assembler-x64.h
@@ -746,6 +746,14 @@ class MacroAssembler: public Assembler {
                 Label* fail,
                 bool is_heap_object);
 
+  // Check if the map of an object is equal to a one of a specified lists map
+  // and branch to label if not. Skip the smi check if not required (object is
+  // known to be a heap object)
+  void CheckMaps(Register obj,
+                 ZoneMapList* maps,
+                 Label* fail,
+                 bool is_heap_object);
+
   // Check if the object in register heap_object is a string. Afterwards the
   // register map contains the object map and the register instance_type
   // contains the instance_type. The registers map and instance_type can be the