Use regular map-checks to guard string-length loading.

src/x64/code-stubs-x64.cc

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 1884 matching lines @@
   } else {
     ASSERT(kind() == Code::LOAD_IC);
     // ----------- S t a t e -------------
     //  -- rax    : receiver
     //  -- rcx    : name
     //  -- rsp[0] : return address
     // -----------------------------------
     receiver = rax;
   }
 
-  StubCompiler::GenerateLoadStringLength(masm, receiver, r8, r9, &miss,
-                                         support_wrapper_);
+  StubCompiler::GenerateLoadStringLength(masm, receiver, r8, r9, &miss);
   __ bind(&miss);
   StubCompiler::TailCallBuiltin(
       masm, BaseLoadStoreStubCompiler::MissBuiltin(kind()));
 }
 
 
 void StoreArrayLengthStub::Generate(MacroAssembler* masm) {
   // ----------- S t a t e -------------
   //  -- rax    : value
   //  -- rcx    : key
@@ skipping 4724 matching lines @@
   __ bind(&fast_elements_case);
   GenerateCase(masm, FAST_ELEMENTS);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64