Use weak cell in monomorphic KeyedStore IC.

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 82c047af5095bdc1a144020647642cc806123e62..465666555bb1276caa8333f81e52b2208e8c0536 100644
--- a/src/x64/macro-assembler-x64.h
+++ b/src/x64/macro-assembler-x64.h
@@ -992,14 +992,12 @@ class MacroAssembler: public Assembler {
                 Label* fail,
                 SmiCheckType smi_check_type);
 
-  // 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,
-                   Register unused,
-                   Handle<Map> map,
-                   Handle<Code> success,
-                   SmiCheckType smi_check_type);
+  // Check if the map of an object is equal to a specified weak 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 DispatchWeakMap(Register obj, Register scratch1, Register scratch2,
+                       Handle<WeakCell> cell, Handle<Code> success,
+                       SmiCheckType smi_check_type);
 
   // Check if the object in register heap_object is a string. Afterwards the
   // register map contains the object map and the register instance_type