ReceiverCheckMode needs to be utilized further.

src/code-stubs.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_CODE_STUBS_H_
 #define V8_CODE_STUBS_H_
 
 #include "src/allocation.h"
 #include "src/assembler.h"
 #include "src/codegen.h"
@@ skipping 1785 matching lines @@
 // preserved, |scratch1|, |scratch2|, and |result| are clobbered.
 class StringCharAtGenerator {
  public:
   StringCharAtGenerator(Register object, Register index, Register scratch,
                         Register result, Label* receiver_not_string,
                         Label* index_not_number, Label* index_out_of_range,
                         StringIndexFlags index_flags,
                         ReceiverCheckMode check_mode = RECEIVER_IS_UNKNOWN)
       : char_code_at_generator_(object, index, scratch, receiver_not_string,
                                 index_not_number, index_out_of_range,
-                                index_flags),
+                                index_flags, check_mode),
         char_from_code_generator_(scratch, result) {}
 
   // Generates the fast case code. On the fallthrough path |result|
   // register contains the result.
   void GenerateFast(MacroAssembler* masm) {
     char_code_at_generator_.GenerateFast(masm);
     char_from_code_generator_.GenerateFast(masm);
   }
 
   // Generates the slow case code. Must not be naturally
@@ skipping 709 matching lines @@
 
 #undef DEFINE_CALL_INTERFACE_DESCRIPTOR
 #undef DEFINE_PLATFORM_CODE_STUB
 #undef DEFINE_HANDLER_CODE_STUB
 #undef DEFINE_HYDROGEN_CODE_STUB
 #undef DEFINE_CODE_STUB
 #undef DEFINE_CODE_STUB_BASE
 } }  // namespace v8::internal
 
 #endif  // V8_CODE_STUBS_H_