[compiler] Remove broken support for undetectable strings.

src/x64/lithium-codegen-x64.cc

 // Copyright 2013 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.
 
 #include "src/v8.h"
 
 #if V8_TARGET_ARCH_X64
 
 #include "src/base/bits.h"
 #include "src/code-factory.h"
@@ skipping 5679 matching lines @@
   if (String::Equals(type_name, factory->number_string())) {
     __ JumpIfSmi(input, true_label, true_distance);
     __ CompareRoot(FieldOperand(input, HeapObject::kMapOffset),
                    Heap::kHeapNumberMapRootIndex);
 
     final_branch_condition = equal;
 
   } else if (String::Equals(type_name, factory->string_string())) {
     __ JumpIfSmi(input, false_label, false_distance);
     __ CmpObjectType(input, FIRST_NONSTRING_TYPE, input);
-    __ j(above_equal, false_label, false_distance);
-    __ testb(FieldOperand(input, Map::kBitFieldOffset),
-             Immediate(1 << Map::kIsUndetectable));
-    final_branch_condition = zero;
+    final_branch_condition = below;
 
   } else if (String::Equals(type_name, factory->symbol_string())) {
     __ JumpIfSmi(input, false_label, false_distance);
     __ CmpObjectType(input, SYMBOL_TYPE, input);
     final_branch_condition = equal;
 
   } else if (String::Equals(type_name, factory->boolean_string())) {
     __ CompareRoot(input, Heap::kTrueValueRootIndex);
     __ j(equal, true_label, true_distance);
     __ CompareRoot(input, Heap::kFalseValueRootIndex);
@@ skipping 338 matching lines @@
   RecordSafepoint(Safepoint::kNoLazyDeopt);
 }
 
 
 #undef __
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_TARGET_ARCH_X64