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 b1f886a140517c2c71457828aac0c8030743d455..91ca845d852caaefed50827dd44f15fbf6bfe152 100644
--- a/src/x64/macro-assembler-x64.h
+++ b/src/x64/macro-assembler-x64.h
@@ -747,6 +747,14 @@ class MacroAssembler: public Assembler {
                 Label* fail,
                 bool is_heap_object);
 
+  // Check if the map of an object is equal to a specified map and branch to a
+  // specified target if equal. Skip the smi check if not required (object is
+  // known to be a heap object)
+  void DispatchMap(Register obj,
+                   Handle<Map> map,
+                   Handle<Code> success,
+                   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